K-Meleon has a problem when more than one rectangle needs to be redrawn. As in, its not. It seems to clear a rectanle big enough to cover all the windows that were previously covering K-Meleon, but then only redraws the spaces under the windows. Easy to fix when working in the browser, just resize, select the text, etc.

Sometimes, also I get the same problem (sorta) when moving a window over K-Meleon in the "Keep contents while moving window" mode thingy jig

This was a mozilla bug, and it has since been fixed. It doesn't happen in the .41 test build.