As the title says: I am going from my rMBP to my iMac (2011) via a thunderbolt - thunderbolt cable. I switch the iMac into Target Display mode via Cmd-F2. This works. However, whenever the rMBP goes to sleep, it loses the second display. The only way to get it back seems to be to unlock the iMac (which also has gone to lockscreen), and re-enter Target mode via Cmd-F2 again. In addition to being a big hassle, all Windows which had been moved to second display are back on the first and need to be re-moved. It's really not worth it. Anyone have a workaround for this? Thanks.