I have found that sometimes the Skeletons swarm multiball becomes a one-ball skeletons swarm. Sear hing the forums I have seen that it is a bug common to mobile plattforms according to a thread in the Android subforum.

The bad thing is that the skeletons swarm does not finish until the multiball ends this meaning that when it becomes a one-ball game it never ends until the ball is lost.

Any idea about when this bug will be removed?