It currently stops the actual move, but it still displays the Pawn drop as a legal move.
Shogi rules are different from Chess, in this respect. In Chess illegal moves can never occur in a game; FIDE rules prescribe that such move should be taken back, and replaced by a legal one. But in Shogi, you just lose. In practice this seems to happen quite often even between club players through dropping Pawns in files that already contain one. The Japanese consider this an important thing: the 81-Dojo server does not refuse illegal Pawn drops, because that would be considered computer help.
So I think it would be logical to add the illegal move that caused game termination to the game record. Otherwise you would never know why the game suddenly ended.
Shogi rules are different from Chess, in this respect. In Chess illegal moves can never occur in a game; FIDE rules prescribe that such move should be taken back, and replaced by a legal one. But in Shogi, you just lose. In practice this seems to happen quite often even between club players through dropping Pawns in files that already contain one. The Japanese consider this an important thing: the 81-Dojo server does not refuse illegal Pawn drops, because that would be considered computer help.
So I think it would be logical to add the illegal move that caused game termination to the game record. Otherwise you would never know why the game suddenly ended.