preg_match function error after permalinks change

I’m getting a php warning appearing in the at the top of my site when I changed permalinks from default to ‘Day and Name’

PHP Warning: preg_match() [function.preg-match]: Compilation failed: nothing to repeat at offset 2 in /home/site/public_html/wp-includes/classes.php on line 210

(same error also for line 211)

Looking at classes.php on line 210-211 it looks like this is when using an anchor (#). I’m not using anchors (#) in my url…
any fix or suggestion of what’s going on? I’d rather not use default with ‘?p=’ especially if i want to use wp_cache for example.

thanks