What did the DROs show when the buffered motion happened?
Also, if you open KMotion, what does the Axis screen show for each axis?
I'm not aware that anything on the KFlop side would buffer motion, but if the Destination value is increasing after the reset, I'd guess the motion request is coming from Mach.
Given the issue happened after the pendant stopped responding, I'd guess that's where the problem lies. I'm guessing that when the pendant has locked up, it's not received the command to flush any outstanding movement, or it simply doesn't flush any motion.
It might be worth doing some testing by commanding a big move via the pendant, and then hitting E-stop before the move has completed, then seeing what happens when you reset Mach.