I think that, now that it has been observed and described in the Help forum, the abuse described here should be outlawed ASAP: Thread 43017
To sum up the scenario: Player A sends Player B a set-piece challenge where A is to move first and can get checkmate in 1. Before Player B can delete the challenge (before B even sees it!), Player A moves and wins. This does not affect either player's rating, but does affect win/loss stats.
At the least, this should be outlawed in the TOS; ideally it should be coded against (the system should delete any challenge which is won by the challenger's first move.)