Windows, regression: The second click of a doubleclick doesn't start autocapture

The second click of a doubleclick doesn't start autocapture. This is a regression from Qt4.

Steps to repro (with sample application from QTBUG-27639):
1) Press left mouse button down on "Disabled" button.
2) Move mouse over to the other window -> Observe no mouse events (this is correct)
3) Release mouse
4) Doubleclick on the "Disabled" button, with keeping the mouse pressed down after the second click.
5) Move mouse over to the other window -> Observe enter and leave events (this is wrong, there should be no events).

The root cause is almost certainly that WM_*BUTTONDBLCLK events are not checked for when starting autograb.