How do I prevent filled pretzels from blowing out? A little while ago I made cream cheese and jalapeno filled pretzels.

I used a standard, mall-style, pretzel dough. 

The filling was cream cheese, cheddar cheese, and minced jalapenos. 

The dough was shaped into balls, allowed to rest and then spread into disks. One or two teaspoons of filling was placed in the center and the dough was gathered around the filling and pinched shut. The pretzels were formed into small logs about two inches long with the seam down.

They were then dipped in a baking soda solution, salted, let proof, and baked at 450F for around 10 minutes.

On baking, the majority of the pretzels burst open and the filling partially leaked out. They were still delicious and were eaten almost instantly by my guests.

How do I prevent my 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