Here is the test case in a unix shell transcript:
johnb@ilinux zsh: cat test.fqn
johnb@ilinux zsh: sort test.fqn
johnb@ilinux zsh: sort --version
sort (GNU textutils) 2.0
Written by Mike Haertel.
Copyright (C) 1999 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
johnb@ilinux zsh: type sort
sort is /bin/sort
It appears as though the -d option is enabled by default. Just my
speculation though. My results on Solaris 2.6 appeared correct.
This was related to the locale stuff, which turned out to be more
confusing than senseful.
It's now (Rawhide/6.2b*) disabled by default.
So how do I disable -d in the interim?
For now, set the environmental variable LC_ALL to POSIX, and sort will work properly.