Qt::WA_TranslucentBackground not working properly

User have experienced a strange behavior if we use Qt::WA_TranslucentBackground to a widget. Its little hard to explain in words, so have attached a sample program and video for issue

Steps to reproduce :

1. Run the attached program.
2. Point to a icon, slider will open. 
3. Now, move the mouse in empty space between icon and slider, then move the mouse  to any side, leaveEvent is not getting called.
4. If you take mouse to slider and then leaves the widget, it is working fine. 
5. Now, comment the line no. 21 in sliderwidget.cpp i.e. m_popup->setAttribute(Qt::WA_TranslucentBackground);
6. Again follow step 3, and it is working fine. 

Expected result : LeaveEvent should not be impacted by WA_TranslucentBackground.