I have had the same problem. I posted about it and sent a message to one of the staff members and never even got a response. I was a bit disappointed that no response was given. I actually thought maybe my opponent was cheating somehow because I was ahead and in a winning situation. Both his King disappeared and his bishop which then began sweeping around the board taking pieces from me. I still wonder if this was some sort of cheat.
Pieces Disappearing
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While playing a 5 minute+2 game today, 11/17/2012, on my iPad, both my pieces and my opponents pieces began disppearing randomly during the game. Additionally, my clock began to run continuously. One of my students also encountered the same problem two days ago while playing on his iPad. In fact, in his game, the opponents king disappeared. I presume this is a glitch in the program on the server end. Can anyone else confirm this behavior?