Hi! Thanks for checking the prototype out, and sorry to hear about this issue you're having.
We've not heard of anyone else having this issue in the past - sounds really weird. If you hit ESC does it bring up the menu?
Are you running the game on a Windows machine? Could you give us any other details that might help us figure out what might be causing this issue?
Sorry again to hear about this, but thanks for letting us know. Hope we can resolve this issue for you!