To keep track of the situation, you need to keep track of which coin is in which position, as well as which side of each coin is showing. Suppose you call the coins x and y. Use the notation to denote that coin x is showing side 1, and similarly and
Suppose that the system starts in the state which means that coin x is at A (showing side 1) and coin y is at B (also showing side 1). After the move is made, the system will be in state If you then make the move the state will become So both coins show side 1, but their positions have switched. Thus and the ambiguity that troubled you has been resolved.