As far as I remember all my pc's, Pentium, I've always had to stop the movie when turning on the subs, and as you say jump to a different part of the movie/episode so that it gets properly synchronized. Don't remember well if the former was always true, but pretty sure the latter yes. I would imagine that not all episode/movies would behave the same, and I would think that it would also behave a bit differently if subs are embedded in the container or not. Also, newer version of MPC have different settings by default than previously, so that might effect something. For example, right now my default setting on playback output is EVR Custom Pres. when I'm pretty sure it used to be one of the VMR.