When the minimumValue of a Slider is updated to larger than the current value of the Slider, the handle position doesn't get the update and hence it is out of range and drawn to the left of the slider (see attached Slider_handle_out_of_range.png).

The attached example can be used to test this. Just click the buttons to set new min and max. Note that if you click the slider first and then the buttons, the problem is not visible.