[Ubuntu 6.06] chown changes file permissions?

# ls -l foo.sh
-rwxr-xr-x 1 root root 23 2007-08-16 14:30 foo.sh
# chmod u+s foo.sh
# ls -l foo.sh
-rwsr-xr-x 1 root root 23 2007-08-16 14:30 foo.sh
# chown root:root foo.sh
# ls -l foo.sh
-rwxr-xr-x 1 root root 23 2007-08-16 14:30 foo.sh
# uname -a
Linux ubuntu 2.6.15-27-686 #1 SMP PREEMPT Sat Sep 16 02:13:27 UTC 2006 i686 GNU/Linux
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