Doh!

I did have something go wrong in the oven.  Apparently the cheap carbon rear end I used had poorly cured chain stays.  I noticed when I mitered them that they gummed up the abrasive belt a little.  Didn't think much of it at the time.  When I pulled the frame out of the oven I noticed this.

OOops...apparently 250F was more than this stay could handle under vacuum.  Good thing it as A)Cheap and B) Only on a test frame.

The odd thing is the at the seat stays from the same set were not affected?

UPDATE:  I've determined that there was uneven heating in the oven which caused the stay to go over temp and collapse.  I've modified the oven with a plate to diffuse the heat from the elements and increased the fan speed with a larger motor.