macOS repeating key events when modifiers are combined

[mjreed-wbd]

Possibly a regression of #6825?

When I press a modifier key, I get a single key-down event as expected. But if I then press another modifier key while holding down the first key, I get a second key down event for the first key in addition to the new event for the new key. If I then release the second key, I get the key-up event for it, and yet another key-down event for the first key. This seems to happen for any combination of modifier keys, including left + right shift, control + alt, etc. and is confusing the heck out of my application.