Something broke in Qt 5.12 preventing MouseMove events to be generated to widgets while pressing 'Control' key down. It seems to be working fine with older Qt versions. Tested with Qt 5.11.2, Qt 5.10.1 and Qt 5.9.7, so some change in Qt 5.12 broke it.

Note: the control key needs to be pressed before mouse is pressed and moved. 

I don't have an example app to demonstrate this, but just create a new QWidget application, add mouseMove event handler to it and log "mouse move!" when it is called. Then press and hold Control key while moving mouse and observe