Scrolling issue with single-column menu when using mouse

Steps to reproduce this bug:

1) Open Windows' "Display" control panel, and go to the "Adjust Resolution" sub-section. Set the Windows desktop screen resolution to a setting that has 900 vertical pixels (e.g. 1600x900 or 1440x900 or etc).

2) Compile and run the attached project (modified Qt Scribble Example)

3) In the Scribble window, click on the Help menu to open the menu. Note that the menu is shown as a single column (as expected), and that the menu is slightly taller than the screen (as expected), so there is a down-scroll-arrow at the bottom of the menu (as expected).

4) Move the mouse down to the down-scroll-arrow at the bottom of the menu.

Actual result:
When the mouse is over the down-scroll-arrow, the menu does NOT scroll down.

Expected result:
Menu would scroll down at this point, so that the user can see the "Dummy 42" and "Dummy 43" entries at the bottom of the menu.

Using the arrow keys to access those entries does work, but they should be accessible using solely the mouse as well.