I haven't played much in hotseat mode, but it may be a bug related to computers. I have seen it happen in all computer games before when testing, but only when playing with fast computers. I didn't determine the root cause though. If you are playing with fast computers you could try disabling it. I'll see if I can pinpoint the cause, now that someone has brought it up.

We were playing without fast computers so far. Also no fast scoring or setup. The only settings we used, was the Factory and a random generated player mat.

I know this is from awhile ago, but I finally found out the bug. I have a function that always assumes the player is the current player turn when you click things in hotseat mode. Basically, I use it in the function I use to move things to the floor line. So, during scoring if a player cannot score a row due to no open spaces(whihc can happen on the random boards a lot) the tiles will be sent to the floor line of the player who's turn will be next. I'm pushing a fix now. Sorry it took me so long to finally fix it!

Edit: The computer's are still not programmed to play the expansion boards though. They can play it, but they don't know how to avoid getting stuck, take advantage of double scoring spots, and they will start rows that can't be placed. Basically, they won't be a challenge on the expansion boards. Maybe I'll add some logic for them in the future.