I was in MP battle with Melvin, alt-tabbed and spent some time replying an email. Came back, clicked on Run for my human warrior and Defeat screen comes up. In the above image, my timer hasn't run down yet (3:55).
Interesting! I wonder if that's due to our client timer getting out of sync with the server version. As of 10.1 flash player does some pretty screwy things with timing when it isn't in the active tab.
Had the same around 10 times and I actually haven't noticed it - still had some time left but defeat screen showed up... I used to afk against AI too often without pop-up which helps a lot now! And the max awaiting timer of course