I hope you didn't just say "OK" and leave them to it again! KEVIN!!! What am I gonna do with you?
I've never come across this one, and I never will because I don't do sets anymore. Group psychology irritates me to no end and I will not put up with it. That kind of reaction is a simple shit test so as always, be persistent and you'll get what you want. I'd just ask, "Oh? And what might that be about?" and let them respond. To which I'd reply with something like "That's cool, as long as you remember where you left off it's all good! Anyway..." and straight into it before they can complain.