Can anyone here help me figure out why gnu tar --exclude and -X are acting funny?

example: I am taring up /var/log. I don't want /var/log/archive/ or /var/log/radacct/. so I try this:

tar -czf mytar.tgz --exclude=/var/log/archive --exclude=/var/log/radacct /var/log

Sounds logical, but tar ignores the --exclude lines (tried just one too to see if that was the problem but no)

I've also tried putting those two directories in a file and

tar -czf mytar.tgz -X excludefile /var/log

but it has the same effect. :-(

Finally I tried this, although I didn't think it'd work at all since the man page says that includes override excludes:

includefile:
/var/log

excludefile:
/var/log/archive
/var/log/radacct

tar -czf mytar.tgz -T includefile -X excludefile

Can anyone help me?

Yes, I've already tried all combinations of removing leading /, adding trailing /, adding /* instead, etc. I don't think that's the problem.

This is GNU tar 1.13. The same thing exists with 1.12 on a much older machine.