actually you've just confirmed that there was no memory leaks(i know some browsers devs would kill for a performance like that) but yes, you have a point..that after 2 many "heavy" tabs were opened, the memory did not revert to its exact setting..that's very normal and that's how windows the operating system allocates memory..kmeleon in that case did not ask for them but windows decided this application is running heavy things so i will leave an extra ram for it to see where it's going..now you can do 2 things so you are rest assured:
same steps you did in your last test and after..wait a little and watch the memory usage going down(this will be slow and will require patience) this will be windows deciding..oh ok, that guy has settled down..let's take back those allocated memory..he obviously no longer needs them
or you can simply minimise kmeleon and the memory will revert instantly to its default setting..restore the window and continue browsing
p.s. if you're concerned with memory usage etc, there's an extension to monitor kmeleon's usage in real time there:
http://kmext.sf.net
(i think it's under enhancements or web development..i'm not sure)