I have no idea if this is a fix or even the same problem, so I'll briefly describe the problem and how I fixed it.
I had a section of spiccato shorts that ended on a Marcato note, and for some reason the Marcato note would sustain without end. It would stop if I went back to the spiccato part, but every time I hit the Marcato note the same thing would happen. This had happened to me before, but I'm not sure how or if I ever did actually fix the problem.
Anyway, the way I fixed this just recently was I accidentally changed my cc controller lane (in Cubase) to 64, and saw that the sustain had been activated. This made no sense to me, as I'm fairly certain I never changed it, though I suppose I might've while messing around with some piano MIDI (could be a bug of some kind activated it I guess). I have no idea, all I know is I deactivated the sustain and I no longer had the problem, and haven't had it since.
So possible solution: check your sustain cc and make sure you haven't accidentally activated it. I know in Cubase it is fairly easy to make changes on the wrong track, which I'm guessing is what I did.