Those are two different issues. The incorrect panel sizing is caused by the desktop pager applet. You can remove it, and the panel width is correct again. Concerning the overlaying elements in the windowlist, this is an old issue which has not been solved until now. A workaround would be to decrease the width of the task buttons and to group similar applications or to use icons only, instead of icons with labels. Those issues appear only if you compile lxpanel against GTK3, which has happened in...