QPushButton popup menus appear on incorrect screen in multi-monitor setup in particular circumstances

The popup menu from a QPushButton can appear on the wrong screen when the situation is like this:

1. Have two monitors, one taller than the other (in my case, one is 1680x1028 and the other is 1440x878). In Control Panel (or equivalent on Windows 10), arrange the windows this way: make the taller monitor the "main display", and align the bottoms of the two monitors. (Basically, the taller/main display needs to have some height over and above the other monitor.)

2. Run a Qt application on the secondary monitor (i.e., the shorter one). Give it a QPushButton that has a popup QMenu. The QMenu should have enough items that it ends up being about half the height of the secondary monitor.

3. Move the application on screen so that the QPushButton is close enough to the top of the monitor that the menu would not fit if it was placed above the QPushButton.

4. Click the button to display the menu – the menu appears on the other display!

It appears that whatever algorithm that determines where to place the popup menu is getting confused by the extra vertical space that is seemingly made available by the other display.