Is there any other factors at play here that may not have been stated above?
Does this occur on a different computer? If you have a 2nd machine to test on I would ask you to try that and see if you can reproduce it there. Also just out of curiosity have you tried a different mouse, and do you have any other problems right-clicking outside of the engine?
I am asking this due to the fact that I am unable to reproduce this on multiple engine versions on multiple machines.
Thank you.