Push-Docking feature leads to bad redraw

Scenario:
1) Open as many windows as will possible to do docking for. That means that for a new window the main windoes hsould "suggest" a place.
2) Double click on title of any window. That window will be undocked. name that windowe as W1.
3) Open one more new window and do docking for it.
4) After that double click on the title of W1. I name it push-docking. The window will be docked yet with re-draw artefacts.

They say that show-hide do the same is room for docking between show and hide was changed.