The problem does not block or delay the user. If the user considers the problem unacceptable the only known way to handle this is to avoid/delay installing Windows 10 Creator Fall update or to uninstall it.
When dragging toolbars or dockable panels there are gray afterimages left behind.As soon as you press the mouse button on a toolbar a gray boundary is drawn around the toolbar. That is normal. The problem now is that this gray rectangle is not or partially undrawn/refreshed as you drag the toolbar. It does not block the user from working and it is a transient problem. but it is inconvenient.
This started with Windows 10 Creator update 1709, fall 2017. The problem is not limited to BricsCAD. We've found the same problem in AutoCAD toolbars and in Acrobat Reader (element properties). The common attribute appears to be that these are all dialogs that are floating / dockable.
At this time it has not been established what the cause is or how it will be fixed.
It may be that a later update of Windows or a display driver may fix the issue. It is possible that a setting in windows can fix it but this has not yet been found.
It is possible that we eventually have to adapt the program to work around the problem.
It is also possible that this is a preexisting problem which now got much worse. Smaller redrawing problems with the boundary rectangles have been encountered in earlier versions of Windows.