How do I prevent filled pretzels from blowing out?
I would suspect that it's steam from the filling causing your pretzels to split during baking. I would try freezing small globs of the filling before cooking, hopefully then it won't get hot enough to steam and split. This is a technique they use in the Momofuku Milk Bar cookbook to make "Bagel Bombs". http://www.amateurgourmet.com/2012/04/everything-bagel-bombs.html