Menu panorama stops spinning after several days

I apologise for posting an issue which is both incredibly unimportant and really awkward to test, but:

I just went on holiday for a week, and accidentally left my computer on with Minecraft on the main title screen. When I got back, the background panorama had stopped spinning. The game itself was not frozen, as the yellow splash text was still changing size and I could still interact with the menu buttons; only the background was frozen.