Mouse event coordinates wrong on drag release (Mac only)

When a drag terminates in macOS / OS X, the combined mouse move and button state change events are unpacked and processed as two separate events. These two events have coordinates that are completely unexpected, and incur problems in apps where inadvertent mouse events are handled and the coordinates are taken as being correct.

I have attached a sample project that demonstrates this using both a pure QML drag operation, and a drag operation that's initiated in C++. Both of them, on mouse release (no matter where), emit the two processed events with incorrect coordinates : mouse move & button state change.

Example output starts with a normal mouse move location, and we initiate a drag:

---------------------- 
 MOUSE MOVE 
local  :  72.0781 ,  209.148
global :  1433 ,  -490
window :  72.0781 ,  209.148
---------------------- 
qml: Cpp Source Rectangle : starting drag
qml: Cpp Source Rectangle : drag ended

… this will be followed by two events, both with incorrect / unexpected coordinates:

---------------------- 
 MOUSE MOVE 
local  :  1367 ,  -962
global :  2728 ,  -1661
window :  1367 ,  -962
---------------------- 
---------------------- 
 MOUSE RELEASE 
local  :  1367 ,  -962
global :  2728 ,  -1661
window :  1367 ,  -962
---------------------- 

Subsequent events now resume to expected coordinates:

---------------------- 
 MOUSE MOVE 
local  :  72 ,  209
global :  1433 ,  -490
window :  72 ,  209
----------------------