Buttons on top of each other in panel

view story

http://www.kubuntuforums.net – Hi, I'm running Kubuntu 13.04 and have even though this is the 2nd or maybe even 3rd version of Kubuntu I use, I still see sometimes that buttons on the panel are placed on top of each other. Most of the time it is okay, it is just rarely that this occurs. In the attached picture you see Chrome and Thunderbird on top of each other. What to do about it? Attached Images Lower KDE panel.jpg (13.8 KB) (HowTos)