I don't see how making ESC print something would provide me with any additional information. I already know that keyboard input gets responded to instantly.
it was the delay from hitting esc to onend displaying anything to the program finishing I was suggesting might be useful.
And debug messages if I can work out a way to see them will almost certainly show me that it freezes at that fullscreen set graphics line.
... write them to a log with a statement when you hit 'esc' during onend(). Again a suggestion because, basically, you have all the code I am having to make guesses.
As for it being some kind of clean up, that was the first thing I suspected but the fact that the delay happens when going from windowed to fullscreen and then never again doesnt really fit that theory.
Unless there is some cleanup when switching for the first time. Again, I haven't got any code to recreate so am guessing.
Anyway, you seem to have it well in hand and seem intent on keeping all the information to yourself so... good luck.