i have a 21.5 inch iMac and after using the expose feature for about 30mins or so it acts strange. i normally use it through the 3rd 'squeeze' buttons on my mighty mouse but it happens with the expose button on the keyboard too. when i activate expose it chucks all the windows out but then brings them all back straight away where before it used to chuck em out n scatter them until i pressed it again. i tried changing the mouse and keyboard and did a software update too but no luck. the same thing happend in my previous 20inch aluminium iMac, any ideas?!