I am finding my progress bar sometimes being all the way full even though the song isn't near the end. I've only seen it a couple of times when it has been paused and coming out of screensaver, but I can't make it happen on demand so it isn't just pausing and the screensaver that causes the problem. My guess is some event is being fired that goes into the code where I set my own isplaying = true when it shouldn't, hence the desire for a property of IsPlaying, then there would be no doubt.
It isn't a big enough problem for me to be overly concerned about, though I'm sure at some point it will bug me enough that I will track it down till I figure it out.