My MBA (13" 10.7.2) has recently developed a problem where it doesn't automatically detect when an external display has been connected or disconnected. For example, I'll open the MBA up, connect a display through the thunderbolt connector, and it won't activate the external monitor until I tell it to ''detect displays," and when I disconnect it, it seems to have no idea that it needs to return to the MBA display being primary. I'm not sure if this is a hardware or software issue (as it works fine 90% of the time after I give it a "detect displays" kick). 
