It turns out this could be recreated by manually editing the cfg.txt to an invalid config and not specifying the track and config in the setup.cfg file.
So you could for example exit LFS on SO6 and manually edit the map name to "Blackwood". Then start a host and the config was wrongly reported on the list of games (and in statistics).
I've stopped this happening with a change on the master server. If any wrong configs are detected, the master server will make that host exit immediately. It's a bit of a rough fix but at least it prevents people driving on "corrupted" hosts and confusing LFS World with invalid statistics.