Override Redirect window doesn't show textures on initial painting pass

Attached is a simple QML file which renders completely transparent, but it should show an image instead.

The simple scene creates an override redirect (BypassWindowManagerHint) window. If one removes the

flags: Qt.BypassWindowManagerHint

the window renders as expected.

From experimenting during investigating this issue in KWin scheduling another repaint directly after the first frame swap fixes the issue.

This seems not to be driver specific and also not to the rendering loop. Also the window manager/compositor seems to have no influence (tested with KWin (all and no compositors) and openbox).

Some more information about the problem can be found in https://bugs.kde.org/show_bug.cgi?id=335270