Huge problem when using external screen on MacBook Pro

I have a problem that doesn't seem to go away. I can't tether now because C1 will not let me resize its window back to laptop size after having had a larger screen plugged in. I use a MacBook Pro and when I edit I plug in a larger 27" screen. When I tether on location I only use the MacBook. C1 now refuses to go any smaller than my last size on the larger screen. Not only does it not recognise the screen is unplugged, which is annoying enough in itself, but what is catastrophic is that it now seems impossible to get it to fit the laptop screen. I have restarted C1 multiple times, I have restarted the computer. Nothing helps. This makes tethering a pain in the rear, to say the least.