By default, pekwm will reorder window list on input focus (probably to optimize things) and this would also reorder buttons inside taskbar. Also, on new window list, all panel buttons would be recreated again, causing many allocations and deallocations. Now, window list received from wm is compared agains internal window storage for diffs.
Fixing this issue made removal some old edewm specific code and made panel nicely working under sawfish ;)