A vanilla Minecraft installation on my Macbook Pro will regularly take my CPU to 100% and keep it there even after quitting. I don't think I'm doing anything particulary demanding with my setting, and in any case, it really does seem as if it's a bug if the game won't quit cleanly.
I'd certainly appreciate any advice on steps I might take to workaround this. I will try a completely clean reinstall just in case previous experiments with resource packs have caused a problem.
Further Information/Update: The problem recurs with a new install, but does not happen on a different map. The safe map is much smaller (a flat world that I use in creative to do redstone experiments); the unsafe map is pretty large I suppose, though hardly enormous and it used to work fine. Is there any possibility of corruption in map data leading to this buggy behviour?