I discovered this one while messing with displaying the Carbon NavCreatePutFileDialog. At some point, this dialog resulting in my SDL application getting SDL_WINDOWEVENT_FOCUS_LOST events. Makes sense, since the Nav open/save dialog could be considered a different window that has "gained" focus.

So I tried calling:

SDL_FlushEvents(SDL_WINDOWEVENT_FOCUS_GAINED, SDL_WINDOWEVENT_FOCUS_LOST);

as well as:

SDL_FlushEvents(SDL_WINDOWEVENT_FOCUS_LOST, SDL_WINDOWEVENT_FOCUS_LOST);

But this DID work:

SDL_FlushEvents( SDL_ALLEVENTS );

I don't know why flushing all events works when trying to flush a specific one doesn't, but I seem to remember running into this before, for other event types too. I've only verified it's a problem for this specific event, but I'm guessing it might be any kind of specific event.