QQuickWidget stays black after being hidden/shown again in QTabWidget

1. Run the attached demo project on Windows 7
2. Click "Tab 2". Observe black background for split second, before the blue rectangle is drawn
3. Click "Tab 1"
4. Click "Tab 2". Observe the black background, with no rectangle being drawn. This happens every time when switching to "Tab 2"

Expected:

• when switching to "Tab 2" for the first time, the background should not be black
• when going back to "Tab 2" (after switching from "Tab 1"), the contents should be correctly displayed

This issue happens after applying the patches from QTBUG-40505 to Qt 5.3.1 sources