It turns out that the particular log I was analyzing may have an illegal move in it. As far as I can tell by my analysis, one player moved a previously moved Rook to his King's space, and the King was not on a space that Rook would move to while castling, though it was a space the other Rook would move to while castling. Since the other Rook was adjacent to it, moving there with it would have been a legal castling move. The result of this move was that the player captured his own King, and this caused errors down the line.
According to the comments in the game, the King's were on the d file, and the Black player was expecting the White player to make the move that appears to be illegal. White's previous move had moved the Rook to the space it would go to while castling, and Black had expected White to castle on that move. So, maybe, I deleted the wrong move from a two-move castle that was made without rule-enforcement. However, changing it to that has changed the opening position, now placing the King on the g file. This is because my code does not yet account for a King castling by moving to the Rook's space, which is how this castling move needs to be written. I will deal with that tomorrow. In the meantime, I will change it back.
It turns out that the particular log I was analyzing may have an illegal move in it. As far as I can tell by my analysis, one player moved a previously moved Rook to his King's space, and the King was not on a space that Rook would move to while castling, though it was a space the other Rook would move to while castling. Since the other Rook was adjacent to it, moving there with it would have been a legal castling move. The result of this move was that the player captured his own King, and this caused errors down the line.
According to the comments in the game, the King's were on the d file, and the Black player was expecting the White player to make the move that appears to be illegal. White's previous move had moved the Rook to the space it would go to while castling, and Black had expected White to castle on that move. So, maybe, I deleted the wrong move from a two-move castle that was made without rule-enforcement. However, changing it to that has changed the opening position, now placing the King on the g file. This is because my code does not yet account for a King castling by moving to the Rook's space, which is how this castling move needs to be written. I will deal with that tomorrow. In the meantime, I will change it back.