For the first time in awhile I have bubbles showing up in my MMF when I roll it out. Any ideas on why?!?

THis has happened to me before when using MMF, and the only thing I've been able to deduce is that it depends on the brand of marshmallows and powdered sugar that I'm using. After several experiments and empirical observations, I've determined that the Safeway brands make for bubbles and sugar lumps (even when well sifted). When I buy them at Walmart or our local Kroger store, no problem. Don't know if that's any help at all...

I think the more you kneed it the more bubbles it gets. Thats what i think from my experience... if theres a way to get rid of them id love to know!