Lately it happens quite frequently that my thunderbolt display remains off when i try to wake my macbook pro (late 2011) in clamshell mode. There is no response on any of the devices connected to the thunderbolt display. When i attempt to wake the MBP with the mouse or keyboard on the MBP itself it just wakes up normally, so it seems that somehow the thunderbolt display loses it's connection to the MBP completely. The only way out from this situation is a reboot. I've changed the setting on the MBP to use only the ATI card, but it makes no difference. Any advice on this?