The problem happens in other profile.d files, and also
in rhel7.

  The issue is that ksh does not set PS1 until reading
profile/initialization files, and only sets it if it is
unset.

  Some initialization files in /etc/profile.d use the
pattern:

# Skip all for noninteractive shells.
[ -z "$PS1" ] && return

at the start of the file, what does not work for ksh.

  I believe this is not a reason to rework ksh
initialization, and the logic should be changed to
check if fd 0 is a tty, for example, as suggested by
the user:

[ ! -t 0 ] && return

or some variant, checking for the "i" character in $-