Assuming an asynchronous UI programming model, I can only conceive this happening because they skipped having a proper Model and instead the View is accessed directly (in the Mode-View-Controller way of thinking).

However the most disturbing thing is that events might get to be processed our of order. Even if you stored current state in a proper Model, there is nothing you can do if your event queue ends up being "<down>, <down>, <enter>".

I guess that's why Qt prefers to do all UI event processing exclusively in a single thread. The event queue will always be serviced in order.