[.]one field for
  each positional parameter that is set. When the expansion occurs in a context where field
  splitting will be performed, any empty fields may be discarded and each of the non-empty
  fields shall be further split as described in Section 2.6.5.

  a() {
          echo $#,1="$1"/$1,2="$2"/$2,3="$3"/$3,4="$4"
          echo $#,'*'="$*"/$*,
  }
  set -- '' 'a' ''
  for f in ' ' '' : ': ' ' :'; do
          IFS=$f ; echo "$*"$* $*; a "$*"$* $*;unset IFS
  done

  --- .1  2025-03-15 23:38:31.359307576 +0100
  +++ .2  2025-03-15 23:38:32.715974215 +0100
  @@ -6,10 +6,10 @@ a a a$
   3,*=aaa/a a a,$
   :a: a  a$
   4,1=:a:/ a ,2=a/a,3=/,4=a$
  -4,*=:a::a::a/ a  a  a,$
  +4,*=:a::a::a/ a a  a,$
   :a: a  a$
   4,1=:a:/ a ,2=a/a,3=/,4=a$
  -4,*=:a::a::a/ a  a  a,$
  +4,*=:a::a::a/ a a  a,$
    a  a a$
   3,1= a / a ,2=a/a,3=a/a,4=$
   3,*= a  a a/ a a a,$

By the very meaning of this [POSIX words] the fields are split individually,
*first*.  This is exactly what i do.
Hence
    echo $#,1="$1"/$1,2="$2"/$2,3="$3"/$3,4="$4"
->
    4,1=:a:/ a ,2=a/a,3=/,4=a
becomes
    :a: -> '' + a
    a -> a
    '' -> discarded (but remembered as it separates fields)
    a -> a
becomes, with IFS=:, when actually creating the argument
    :a:a::a
becomes the actual argument
    < a a  a>

  +                       /* In order to be compatible with bash, NetBSD sh and NetBSD ksh, at minimum, we need to
  +                        * deviate from POSIX standardized behaviour, and field split the quoted variant instead!
  +                        * This applies to $@ as well as $* */
  +                       if(*spcp->spc_ifs != '\0' && !su_cs_is_space(*spcp->spc_ifs)){
  +                               cp = n_var_vlook(n_star, TRU1);
  +                               goto jfs_split;
  +                       }
  +
  +                       /* In all other cases individually field split the expanded parameters */

$ printf ',l\nq\n' | ed test.sh
178
a() {$
\techo \$#,1="\$1"/\$1,2="\$2"/\$2,3="\$3"/\$3,4="\$4"$
\techo \$#,'*'="\$*"/\$*,$
}$
set -- '' 'a' ''$
for f in ' ' '' : ': ' ' :'; do$
\tIFS=\$f ; echo "\$*"\$* \$*; a "\$*"\$* \$*;unset IFS$
done$
$ env -i POSIXLY_CORRECT=1 sh -c 'for i in sh posh ksh mksh lksh loksh dash bash yash "busybox sh"; do qfile -v `command -v ${i% *}` ; $i test.sh >|"test_${i}.txt" 2>&1; done'
app-alternatives/sh-0: /bin/sh -> lksh
app-shells/posh-0.14.1: /bin/posh
app-shells/ksh-1.0.8: /bin/ksh
app-shells/mksh-59c: /bin/mksh
app-shells/mksh-59c: /bin/lksh
app-shells/loksh-7.6: /bin/loksh
app-shells/dash-0.5.12-r1: /bin/dash
app-shells/bash-5.2_p37: /bin/bash
app-shells/yash-2.57: /bin/yash
sys-apps/busybox-1.36.1-r3: /bin/busybox
$ sha1sum test.sh *.txt | sort
031cf59fcbcfc7eede60e35c9ede332bbb962f35  test_posh.txt
7edcc231165d9b3ca2f875501c02e4f8eff73e6b  test_loksh.txt
88acd3756f017d1f74d5bb62cfa9a0f0e72a08ee  test_bash.txt
a947a1ebd8dc2fcfc1068359836fc6a224a13ccb  test_busybox sh.txt
a947a1ebd8dc2fcfc1068359836fc6a224a13ccb  test_dash.txt
a947a1ebd8dc2fcfc1068359836fc6a224a13ccb  test_ksh.txt
a947a1ebd8dc2fcfc1068359836fc6a224a13ccb  test_yash.txt
c7f2494ab0f12315513dfc2a70ab24d693dd6592  test_lksh.txt
c7f2494ab0f12315513dfc2a70ab24d693dd6592  test_mksh.txt
c7f2494ab0f12315513dfc2a70ab24d693dd6592  test_sh.txt
ce30bb2a9eafa825dcd67be9a60e49529f091166  test.sh
$ diff -u test_posh.txt test_loksh.txt
--- test_posh.txt       2025-03-18 12:16:56.797930657 +0100
+++ test_loksh.txt      2025-03-18 12:16:56.822930552 +0100
@@ -1,9 +1,9 @@
  a  a a
 3,1= a / a ,2=a/a,3=a/a,4=
 3,*= a  a a/ a a a,
-a a   a
-2,1=a a /a a ,2= a / a ,3=/,4=
-2,*=a a  a /a a   a ,
+a a a
+3,1=a/a,2=a/a,3=a/a,4=
+3,*=aaa/a a a,
 :a: a a
 3,1=:a:/  a ,2=a/a,3=a/a,4=
 3,*=:a::a:a/ a  a a,
$ diff -u test_posh.txt test_bash.txt
--- test_posh.txt       2025-03-18 12:16:56.797930657 +0100
+++ test_bash.txt       2025-03-18 12:16:56.837930489 +0100
@@ -1,15 +1,15 @@
  a  a a
 3,1= a / a ,2=a/a,3=a/a,4=
 3,*= a  a a/ a a a,
-a a   a
-2,1=a a /a a ,2= a / a ,3=/,4=
-2,*=a a  a /a a   a ,
-:a: a a
-3,1=:a:/  a ,2=a/a,3=a/a,4=
-3,*=:a::a:a/ a  a a,
-:a: a a
-3,1=:a:/  a ,2=a/a,3=a/a,4=
-3,*=:a::a:a/ a  a a,
+a a a
+3,1=a/a,2=a/a,3=a/a,4=
+3,*=aaa/a a a,
+:a: a  a
+4,1=:a:/ a ,2=a/a,3=/,4=a
+4,*=:a::a::a/ a  a  a,
+:a: a  a
+4,1=:a:/ a ,2=a/a,3=/,4=a
+4,*=:a::a::a/ a  a  a,
  a  a a
 3,1= a / a ,2=a/a,3=a/a,4=
 3,*= a  a a/ a a a,
$ diff -u test_bash.txt test_dash.txt
--- test_bash.txt       2025-03-18 12:16:56.837930489 +0100
+++ test_dash.txt       2025-03-18 12:16:56.830930519 +0100
@@ -4,12 +4,12 @@
 a a a
 3,1=a/a,2=a/a,3=a/a,4=
 3,*=aaa/a a a,
-:a: a  a
-4,1=:a:/ a ,2=a/a,3=/,4=a
-4,*=:a::a::a/ a  a  a,
-:a: a  a
-4,1=:a:/ a ,2=a/a,3=/,4=a
-4,*=:a::a::a/ a  a  a,
+:a: a a
+3,1=:a:/ a ,2=a/a,3=a/a,4=
+3,*=:a::a:a/ a a a,
+:a: a a
+3,1=:a:/ a ,2=a/a,3=a/a,4=
+3,*=:a::a:a/ a a a,
  a  a a
 3,1= a / a ,2=a/a,3=a/a,4=
 3,*= a  a a/ a a a,
$ diff -u test_dash.txt test_lksh.txt
--- test_dash.txt       2025-03-18 12:16:56.830930519 +0100
+++ test_lksh.txt       2025-03-18 12:16:56.813930590 +0100
@@ -6,10 +6,10 @@
 3,*=aaa/a a a,
 :a: a a
 3,1=:a:/ a ,2=a/a,3=a/a,4=
-3,*=:a::a:a/ a a a,
+3,*=:a::a:a/ a  a a,
 :a: a a
 3,1=:a:/ a ,2=a/a,3=a/a,4=
-3,*=:a::a:a/ a a a,
+3,*=:a::a:a/ a  a a,
  a  a a
 3,1= a / a ,2=a/a,3=a/a,4=
 3,*= a  a a/ a a a,

$ sha1sum test_ksh88.txt
c615e994262cb2a6a6469a0f967ae8feeaa40966  test_ksh88.txt
$ sed -n l test_ksh88.txt
 a  a a$
3,1= a / a ,2=a/a,3=a/a,4=$
3,*= a  a a/ a a a,$
a a   a $
2,1=a a /a a ,2= a / a ,3=/,4=$
2,*=a a  a /a a   a ,$
:a: a  a$
4,1=:a:/ a ,2=a/a,3=/,4=a$
4,*=:a::a::a/ a  a  a,$
:a: a  a$
4,1=:a:/ a ,2=a/a,3=/,4=a$
4,*=:a::a::a/ a  a  a,$
 a  a a$
3,1= a / a ,2=a/a,3=a/a,4=$
3,*= a  a a/ a a a,$

set a: a
IFS=:
printf '[%s]\n' $*

[a]
[a]

[a]
[]
[a]

When the expansion occurs in a context where field splitting will be performed, any empty fields may be discarded and each of the non-empty fields shall be further split as described in [xref to 2.6.5].

When the expansion occurs in a context where field splitting will be performed, these initial fields shall be further processed in the same manner as for the '*' special parameter.

When the expansion occurs in a context where field splitting will be performed, any empty fields may be discarded and each of the non-empty fields shall be further split as described in [xref to 2.6.5]. When the expansion occurs in a context where field splitting will not be performed, the initial fields shall be joined to form a single field with the value of each parameter separated by the first character of the IFS variable if IFS contains at least one character, or separated by a <space> if IFS is unset, or with no separation if IFS is set to a null string.

When the expansion occurs in a context where field splitting will not be performed, the initial fields shall be joined to form a single field with the value of each parameter separated by the first character of the IFS variable if IFS contains at least one character, or separated by a <space> if IFS is unset, or with no separation if IFS is set to a null string. When the expansion occurs in a context where field splitting will be performed:

• If IFS is set to a null string, any empty fields may be discarded but no further processing shall be performed.


• Otherwise, any empty fields may be discarded and the remaining fields shall be processed in one of the following two ways:
  
  
  1. Each of the non-empty fields shall be split as described in [xref to 2.6.5].
  
  
  2. The remaining fields shall be joined to form a single field, as described above for expansion in a context where field splitting will not be performed, and this field shall then be split as described in [xref to 2.6.5].

<small>NOTE: These two alternatives produce different results if IFS begins with a non-whitespace character and a positional parameter, other than the last one, ends with a non-whitespace IFS character. Joining before splitting produces an extra empty field (after the fields that splitting each field separately produces for that positional parameter). A future version of this standard may require that this extra empty field is not produced.</small>

The Korn shell changed the way $* is expanded between the 1988 and 1993 versions, when subject to field splitting: ksh88 first joined the positional parameters as if $* were quoted and then performed field splitting on the result. This produced an extra empty field if IFS begins with a non-whitespace character and a positional parameter, other than the last one, ends with a non-whitespace IFS character. For example:

set a: a; IFS=:; printf '[%s]\n' $*
[a]
[]
[a]

The natural expectation is that expanding $* here would produce the same fields as expanding $1 and $2 as separate arguments:

set a: a; IFS=:; printf '[%s]\n' $1 $2
[a]
[a]

and this is what ksh93 does. Since David Korn was involved with development of the shell language requirements in POSIX.2-1992 at the same time that he was working on ksh93, it is believed that the intention was for POSIX.2-1992 to require the ksh93 behavior, but the wording was not sufficiently clear and some shells have continued to behave like ksh88. This standard now explicitly allows both behaviors (and likewise for $@ when subject to field splitting). However, implementors of shells that behave like ksh88 are encouraged to change to the ksh93 behavior.