Andy, they're just messing with you. It's a glitch in the program. Write chess.com and let them know.
I have a similar issue with my opponents moving their pawn diagonally, and all of a sudden my pawn right next to it disappears! That's crazy too, no?
That's en passant.
That's
that how kco's view of Australia, yay we are at top, that why we are called the top end.