The behaviour is actually broken on RHEL3, not RHEL4.

+++ This bug was initially created as a clone of Bug #203339 +++

psset will generate broken PS output when used on RHEL4.

1. Run
ls | a2ps -o - | psset -t > test.ps
2. Notice the broken ps on RHEL4 (where it works on RHEL3)

The bug (control characters where there should be text) is due to a change in
sed's behaviour.

RHEL3, sed-4.0.7-3:
$ echo ''|sed -e ' i\\co' | hexdump -C
00000000  5c 63 6f 0a 0a                                    |\co..|
00000005

RHEL4, sed-4.1.2-4:
$ echo ''|sed -e ' i\\co' | hexdump -C
00000000  0f 0a 0a                                          |...|
00000003

RHEL4, with RHEL3's sed:
$ echo ''|./sed -e ' i\\co' | hexdump -C
00000000  5c 63 6f 0a 0a                                    |\co..|
00000005

-- Additional comment from pmachata on 2006-08-22 13:36 EST --
Hmm... yes, there indeed is a change in behavior.  However it seems to me that
the new version is correct in handling backslashes, and that the right way to
write the sequence '\co' is with 'i\\\co'.  First '\' is the delimiter (which
can be missing, but if it's here, it has to be the delimiter), following '\\' is
escaped backslash, and then 'co'.  In contrast, 'i\\co' interprets \c as escape
and turns 'o' into control character.
If you retarget this bug against EL3, I will adjust the behavior of sed there.