I was playing on Linux. And to clarify what was happening, I can't turn all the way around. I can look slightly to the left and right, but that's it. When I pause the game, the mouse cursor is all the way at the edge of the screen; when I move the mouse cursor to the middle of the screen and unpause, then I can look slightly further in whatever direction I was trying to look. It's almost like the cursor's getting stuck on the side of the screen? I'm not sure.
Hopefully, this helps. I'm bad at describing bugs. ^^;