Due to tiling (see issue #21) it is usually quite hard to make one window overlap another one, if both windows are in the same container, but it's possible and very usual if a window opens some other windows as it's descendants.
So when you close a window that was overlapping another one - a repaint event is necessary, but it doesn't happen, so you may end up with dead window's remains still being drawn.
I've experienced this already quite a number of times, but at the moment I can't provide firm steps to reproduce the issue.
I see a "TODO: need to check" label. Does it mean you've already made an attempt to fix this issue but not sure whether the bug is gone? or does it mean that you couldn't yet reproduce it?
Due to tiling (see issue #21) it is usually quite hard to make one window overlap another one, if both windows are in the same container, but it's possible and very usual if a window opens some other windows as it's descendants.
So when you close a window that was overlapping another one - a repaint event is necessary, but it doesn't happen, so you may end up with dead window's remains still being drawn.
I've experienced this already quite a number of times, but at the moment I can't provide firm steps to reproduce the issue.