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.