I did some troubleshooting on a few playback issues and I hope I've fixed all the playback gremlins that were hiding in the code. I found the bug where if the first thing you do after opening a sequence is hit the play button and you didn't see the play marker line moving across the screen. That turned out to be an uninitialized variable in the Timeline class that made it think you had clicked in the timeline to initiate play so it returned an invalid play start time of -1. I fixed the bug that Gerry found where if you paused model playback and dropped an effect and then un-paused the play marker line wasn't moving. I also found when model playback was paused there was code that would stop playback but without calling the proper method that shuts down the media playback so it left it in a bad state. That one was triggered by an event when effects were unselected so it was a race condition as to which of two events got processed first as to whether it messed up playback or not. So let me know if you find anymore weird things.
Just remember we have two playback modes. Effect Play just renders the effects without playing the audio so it's the preview playback you get when selecting an effect. Model Play is when you press Play and the sequence is playing. If you pause Model Play and then drop an effect then I'm canceling Model Play and initiating Effect Play. You can Pause Effect Play and then Pause or Play will UnPause it. It can get confusing because you could be in Effect Play and hit Pause, then hit Play which will resume Effect Play, and then hit Play a second time and then Model Play is initiated. I'd almost like to have somewhere that I can show the playback mode.
