The problem you're describing with mintmenu is normal. Mintmenu is in reality a fork(?) of USP menu developed as a third party project for Ubuntu. It's designed as a much more flexible, attractive alternative to SUSE's SLAB menu introduced with SLED 10. But, I digress. The pause following new program installation occurs when mintmenu updates itself to show the new software you've installed. As for your memory leak issues, I don't seem to have that problem with my installation. I'm using Mint 3.1 with Daryna's packages for mintmenu, mintupdate, mintdesktop...etc. If you're not using Daryna, then perhaps you should update to that version of Mint's applets and see if that helps improve your mintmenu experience. To grab the latest versions of the "mintiness" go to: http://www.linuxmint.com/repository/daryna/
Note: i don't recommend you add Daryna's repository to your sources.list file (if you're running 3.x) Good luck!