Some tracks stop producing sound all of a sudden?

I'm running the trial version of Sonar X1 Producer, and I've noticed that every once in a while, some of my tracks will stop producing sound. For no reason. I'll solo those tracks, but won't hear anything. I take the clips in those tracks and move them to other tracks, and they play fine. I take clips from other tracks and bring them into the damaged tracks, and of course they will not play. The only solution is the close the project and re open then.

Is this solved in X1c? Am I doing something wrong?