Mmm... I don't know what's going on. After upgrade to 2.8 it doesn't work at all. My Contributor can register as many posts as he/she wants (limit is set by USER_ID). In my opinion it's not just related with "any" type. As I remember last working plugin version was 2.4. I'll try to install fresh copy of WP and then try to install 2.8. Maybe something is wrong with update process. Any ideas?
Ps. Could You tell me where Your plugin keeps limits? During uninstall process limits seems not to be deleted. After reinstall I can see my limits from previous version.