Recently I've played a bit on MP servers, and I've ran into this problem... Basically, sometimes, at some point, it just happens that I can't drag any items around my inventory, or from the inventory to chests, furnaces, etc... Basically if I click and drag an item it's the same thing as if I wasn't clicking, I get no response and nothing moves around. This has only happened to me in MP, since I rarely play SP at the moment, but when I get BACK to SP, without restarting Minecrat, the problem persists.
Everything else works, except moving things around. This is fixable by restarting Minecraft, but I would rather not, it's annoying.
I'm on a MBP, 13'', running OS X Snow Leopard 10.6.7, in the latest version of minecraft.
Cheers
PS: I also get the annoying black screen bug when playing in-browser, but that's a different story, and it seems that it hasn't been fixed for... around a year or so... Just sayin'















