We thought it would be a good idea to bring this bug to your attention, since it has the potential to severly hamper your enjoyment of this (or any Unity built) game.
Take a look at this picture, we will explain how to avoid it at the bottom of this post.
This bug takes place when the player is running the game in fullscreen mode in a non-native resolution. The easiest way to avoid this is to simply play in windowed mode or in the highest resolution your monitor supports.
You can find a bug report about this on the official Unity issue tracker here