APC is leaking

I'm not sure if this is a bug, or is just a bad config on my part and should be a support request.

APC appears to be 'leaking' user cache entries across drupal sites running on the same server. If more than one drupal site is using APC, then there are some instances where one site appears to be loading the cache from the other site. Very strange behaviors result - pieces of the other site's theme appears, strange errors are popping up - as you can imagine things really start breaking pretty quickly.

Has anyone else run into this problem?

Thanks!