QTimer period unstable in Qt 5.12.0 when mouse cursor movement over widget (compared to Qt 5.9.6)

 
Hi,

I moved my code from Qt 5.9.6(msvc15) to 5.12.0(msvc17) and noticed that
QTimer slows down when I move mouse cursor over a window area (example code attached)

When I run my example in 5.9.6 'avg' times stay at 2ms and 50ms at all times.

When I run the example in 5.12.0 'avg' times rise during cursor movement(as well as dial update).

This picture shows 'avg' times without cursor movement:

This one shows 'avg' time with cursor movement. In case of QTimer period of slot calls rises from 2ms to nearly 5ms.

Why this different behaviour between 5.9.6 and 5.12.0 ?