Yep that one is a real pain. I don't know why it doesn't just recognise it's not getting anywhere and stop, saving what it has done. I think usually it does save when you force quit it though, which is lucky given that the slow down tends to pretty much lock up the whole system.
The same thing happens in DVD Player sometimes, usually leading to a forced restart in my experience. I agree that there must be a better way... but I don't think one is implemented yet - something like the old cmd-. for stop would be nice.