This looks like an old issue.
I can reproduce this on my son's MacOS X 10.4, in ksh93 release p:
{
rm -rf /tmp/command /tmp/builtin
umask
mkdir -m 1777 /tmp/builtin
/bin/mkdir -m 1777 /tmp/command
ls -ld /tmp/command /tmp/builtin
rm -rf /tmp/command /tmp/builtin
} > test.out 2>&1
$ cat test.out
0022
drwxrwxrwx 2 henk wheel 68 Apr 7 17:49 /tmp/builtin
drwxrwxrwt 2 henk wheel 68 Apr 7 17:49 /tmp/command
$ echo ${.sh.version}
Version M 1993-12-28 p
$ uname -a
Darwin xxxx.local 8.11.1 Darwin Kernel Version 8.11.1: Wed Oct 10
18:23:28 PDT 2007; root:xnu-792.25.20~1/RELEASE_I386 i386 i386
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