I have lost count of the number of times I have waited for an opponent on PvP, decided that I did not wish to wait any longer, and pressed the 'back to menu' button, only to have an opponent show up JUST before the clicking (or even DURING the clicking), and automatically lost that match.
A simple solution is to disable the 'back to menu' button for a very short time (e.g. half a second) when an opponent is found.