QSlider does not process lose of focus in a specific circumstance:

1. Left-click, hold, and drag the slider handle to a new value
2. With the left mouse button still held, right-click outside the slider control area
3. Release the left mouse button

Slider still appears as if mouse button is held. Focus-dependent signals (such as valueChanged) are not emitted. If tracking is off, valueChanged signal is never emitted and new slider value is not recognized.