Dock shows up while in game build because mouse isn't locked to screen centre
I apologize for the delay in response. I entered a bug report for this and I believe it has been fixed as of 4.2.1. If you are still experiencing this issue after updating, please let us know. Thanks!
answered Jun 26 '14 at 05:18 PM
Follow this question
Once you sign in you will be able to subscribe for any updates here