Gui does not refresh properly evene after processEvents() is caled

When OpenGLWidget is used and processEvent() is called, Gui does not alwys refresh properly with Qt5.15 but does works with earlier version like 5.9.5 and 5.12.

Attached is the sample application: and steps

. run GuiRefreshTest.zip

. Hover the mouse over the "Run GL Test" button

. Press/Release LMB to trigger the button

. Notice that the test begins:

• Label changes from "Test: Not Active" to "Test: Active"

• GL Qt logo spins 360 degrees

• Progress bar updates

• The "Run GL Test" button is disabled

. Notice that the GUI appears to "freeze" near 99-100%

• Label does not change back to "Test: Not Active"

• The "Run GL Test" button is never re-enabled

. Return the mouse back to the surface it was on (this will trigger mouse move events).

. Notice that the GUI finally updates

This works on some graphics card but can be reproduced on Nvdia card GeForce GTX 1060 or similar