OSX: windows behind the active window receive move events, even if the mouse is over the active window

On OSX, if you have two partially overlapping windows and move your mouse from the inactive one to the active one, the inactive one continues to receive move events.

The attached application demonstrates this. It opens two windows which are partially overlapping, and prints the events each of them receive.
To reproduce:
1) start your mouse over the left one (which is behind the right one)
2) move your mouse over the right one without leaving the rect of the left one (so the mouse goes directly from being over the left window to being over the right)
3) observe that the left (inactive) one continues to receive mouse events, while the active one does not:

// Window 0 is the left (inactive) one. Here I'm moving the mouse
event  QWidget(0x106934830, name = "Window 0")   5 
event  QWidget(0x106934830, name = "Window 0")   5 
event  QWidget(0x106934830, name = "Window 0")   5 
event  QWidget(0x106934830, name = "Window 0")   5 
event  QWidget(0x106934830, name = "Window 0")   5 
event  QWidget(0x106934830, name = "Window 0")   11 
event  QWidget(0x106934830, name = "Window 0")   5 
// Here Window 1 (active/topmost) gets the Enter event, and so should now be receiving Move events
event  QWidget(0x10453a940, name = "Window 1")   10 
// Instead, window 0 continues to receive the Move events
event  QWidget(0x106934830, name = "Window 0")   5 
event  QWidget(0x106934830, name = "Window 0")   5 
event  QWidget(0x106934830, name = "Window 0")   5 
event  QWidget(0x106934830, name = "Window 0")   5 
event  QWidget(0x106934830, name = "Window 0")   5 

This seems to be a consequence of using NSTrackingActiveInActiveApp in qnsview.mm, and passing Move events through without checking to see if the window is the topmost window under the mouse. Both NSViews receive the move events, but only the first one to receive it gets the event all the way through to the QWidget.