I just got a new rMBR early 2015 and it works great until I plug in an external monitor. When I do that the mouse and keyboard freeze for a second at a time pretty often. The entire system doesn't freeze because video or sound won't stop, only input stops. This doesn't happen when only using the built in display, and happens whether or not I use an external keyboard and mouse or built in keyboard and mouse. I need to figure this out because it's REALLY annoying.