Regression: Leave and enter events are not generated for non-native widgets when there is a popup open

In Qt4, whenever there is a popup open, leave and enter events are still generated for widgets when mousing over them. In Qt5, this is only the case with native widgets.

Use the attached application to see the issue:

1) Click "Popup" button -> leaves are generated for the widget stack at that location (this is correct)

2) Move mouse so that it is still over "Popup" button -> No enter is generated. Enters should be generated for the widget stack at that location on first mouse move after opening the popup.

3) Mouse over various other widgets -> no leave and enter events are generated for other widgets as is expected.

Uncomment the following define in mainwindow.cpp to enable native widgets:

#define NATIVE_WIDGETS

Repeat the steps with native widgets enabled -> leave and enter events are generated for widgets in step 3). Step 2) also fails for native widgets.

Note: For test case, expand tst_QWidget::underMouse().