when i disconnect from a single player world to freezes and turns black and its stuck on my MAC dock

Put the summary of the bug you're having here

What I expected to happen was...:
it would have normally exited mine craft

What actually happened was...:
it wouldn't let me exit and now its stuck on my dock it happened 5 times now. now i have 5 crafting tables on my MAC dock and i can't quit them either pls help mine craft is making my computer crash PLEASE

Steps to Reproduce:
1. create new world on MAC air book the big one
2. press esc then click disconnect it will either disconnect or freeze if it freezes then it will be stuck on your dock
3. if it didn't happen then wait 1hour and try again this happens a lot but sometimes it won't