I've had that before, where it (emax material) even came up to the top of the ring. Since it was only a single unit, and I caught it in time (the plunger distance going past normal) I stopped it and was able to use the unit. I had previously been using plungers from Zubler, with no problem, then went to Microstar, and started having problems. I believe they both get them from the same place (Microstar?) but the Zubler rep said theirs are better, more consistent. I'm not sure if it is sales pitch or not. I do still get some creep up the side of the Zubler plunger once in awhile, but nothing that would make me want to switch back to alox plungers and their higher reaction layer.
I also bought some new tops and sprue bases from Ivoclar, just in case my old ones were wearing out and causing there be more space between the plunger and the side walls. When I see it pressed good, I mark the bottom of the ring "good" with a Sharpie, so I'll know on following presses if there is a higher creep issue, it's the plunger (I use Microstar for large rings, and Shofu Ceravety for small rings).