- Joomla 1.5 RC 1 SEO has a bug that has been reported to joomla core team in bug tracker (still open state). See readme file
- Joomla 1.0.13: I just tried reproducing problem, without success.
Could you please give more details on the SEO used, etc ?
Also don't forget to rename, but also EDIT the .htaccess file if you are running from a subdirectory, to edit the RewriteBase directive in it