Yes it was the positve side that I was soldering at the time. It is also the side that blew off. The negative side is severly bulged and was supported by the battery jig. There is no evidence of shorting. The shrink wrap and label around the cell still looks brand new. No burn marks what so ever. I even double shrinked wrapped these cells. Plus I had the iron on top of the battery bar making it even more difficult to short it. Even if it was a short, it would have to be shorted for much longer than the few seconds I had the iron on it before it blew. And yes the polarities were correct. There were about seven people in the general area at the hobby shop when it happened and no one noticed anything unusual about the pack.
The cells were at room temperature when I was building them.