If you press the spacebar (presumably to pause) during playback of the tutorial videos, the game locks and you cannot resume normal operation. In this particular case I had:
1) Started the game
2) Clicked Tutorials
3) Double-clicked the second tutorial
4) alt-tabbed out (in windowed mode)
5) alt-tabbed back in
6) Hit spacebar on a whim
7) Game froze
Only way I could quit was to click the close window button in the upper right of the window and let Windows bring up the error dialog and close the program out. Yes, I have the latest update installed, and yes I restarted after doing so, and yes I'm using stardock central.
Reproduceable: 100% of the time
It does not appear that alt-tabbing makes any difference, when I did it happened and when I didn't it still happened.