I did wonder this, but can't find very much about it. I can just avoid gluten free bread that looks like it has powder on the top, but if it does that to my lips I am just worried if it's upsetting my tummy too.
@gurgi I would look at the ingredients and go through that list to see if an allergic reaction is possible.
Regarding m and s soft rolls: I did a search on the ingredients of the gluten free version. It has added B vitamins (b2, b5, and b6). I also see that niacin (b3) was added. Sometimes when people take b3 or, really, too much of it, they get a flush.
Again, go through the ingredients, try to figure out what constitutes that powder on the tops of the breads, and see if it could be causing a reaction.