I have issues with Kopete if I don't close the app for a first time and just straight reboot. If I close it with the new window size, it then is saved. This would be interesting to fix, as would be the issue where new windows just randomly popup everywhere instead of centered.
In Control Center, Desktop, Window Behavior, Moving tab, is Placement set to Center or Smart?
I have always found the alleged Smart setting to ve ratehr dumb and infuriating. :)
Darrell