Originally Posted by Moe Zhoost

Tubes have only one seam, where the two ends are joined together. What you are probably referring to is a flash line created during the vulcanizing process. This flashing has no inherent weakness and thus does not fail. What you observed were probably small air bubbles from the original wire puncture migrating along the flashing line until large enough to become visible. I'd predict that if you had repaired the original wire puncture, the tube would have been just fine.

https://www.youtube.com/watch?v=xyck0QTbodo