I got annoyed problem with KWin while minimizing some windows. I opened Libreoffice Calc and typed in some cells, and it zoomed to center when I minimized. That sometime happened in group windows like Pidgin, Skype, Libreoffice-Writer, Thunderbird even KDE Applications.
I tried to search for solution but found nothing. I tried on Laptop, PC, netbook and got the same problem.