The size of the docks inside KMainWindow has not been saved in the following use case:
- open an application which has several docks
- resize the docks without resizing the window or adding/removing docks
- close the application

This has been fixed now.
Implementation note: installing the KMainWindow as event filter by dock->installEventFilter(this) and overwriting QMainWindow::eventFilter() did not work inside KMainWindow::event().