If the empty seat posted the BB and everybody folded, theoretically "the ghost" could have won the pot without any cards LOL!! It would have been nice if you convinced other players to do this just to see what happened. Then you can always contact admin and get the whole game (or the offending rounds) reversed. Other possibilities:
1) Bug - this is rather disturbing because if a bug that obvious exists how safe is play on that site anyway?
2) Live Testing - they were testing something on a live game - again disturbing and the rest is as 1) above.
3) There was a player in the seat but somehow stayed invisible - this is a specific type of a bug or is part of the code programmed with some purpose in mind - even more disturbing and the rest like 1) above.
I have seen some very strange things happen with online play over the years. That is why buggy software or outright fraud puts this industry still at a very early stage of development. Regulation that at the lowest level would require extensive code testing an fraud prevention would help a lot - this is only in my humble opinion - others might like the unregulated nature of the software, especially if they happen to benefit from it.
Edited by TomTheGnome (Tuesday, May 20, 2014 @ 13:33 GMT)