 <p>I solved this problem by playing around with my display settings. I had my iPad connected to my MacBook using Air Display. Disconnecting the iPad with Interface Builder windows left on it seems to leave those windows in "la-la land." Even re-connecting the device didn't seem to work. I had to open the Display preferences, choose "Detect Displays" and then choose "Mirror Displays". After that I de-selected "Mirror Displays" and closed out Interface Builder. Opening Interface Builder again brought the window back, but it was on my external display. </p> <p>I think this is a bug in the sense that Apple should figure out a way to put all the windows back on the main screen once you detach the external one.</p>