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.  ^^;