The past few times I have made MMF I have these weird little gelatin looking clumps. What am I doing wrong and what are they?

I've never had that happen...maybe your marshmallows aren't melted all the way?

I've noticed HEB powdered sugar isn't cane sugar but walmart's powdered sugar is. I know some people say that bad things will happen if you try to make MMF with beet sugar instead of cane sugar. (they never say what, though)

I always make mine with the mixer. The only problem I've had with it was one time when I put the sugar in first, then the marshmallow on top. I ended up with hard lumpy sugar packed into the bottom of the bowl. I managed to salvage that batch, but it wasn't nice the way it usually is.

I melted the marshmallows till they were all soupy and still the clumps. I have used the HEB and Domino brand powdered sugar and same thing. Somebody help!