Puffed, but why?

[cLaWz]

Picked up my SMC 2S 24C 2600mah battery at the Texas Twister event back in February. I have used it as my backup/qualifying pack in my Slash since it was the smaller of my 2 batteries (other is a 4000).

Locally our slash quals are 5 minutes with 7 minute mains on a small track. Charged the pack the other night and ran it for a qualifier. When I pulled the battery I noticed the case had popped open on one end. I figured the casing glue just came loose since it went back into place easily. Ran one more qualifier after recharging and noticed the pack did it again but this time felt "squishy" if you will. Seeing as how I had done my research on lipo I knew it was puffed but I cannot figure out why.

Setup is a bone stock Slash run in the Slash Spec Class (only change is Deans connectors).
Track can be seen here - http://www.youtube.com/watch?v=jO68BXDa2_M

Pack is 6 months old and has always balanced perfectly. Never overcharged, overdischarged or had any issues with it until this.

Any ideas?

[cLaWz]

Pictures

Let me reiterate, this pack was a backup pack that has never been bashed (have 2 NIMH packs I use for that) always balanced, and only used once or twice a week at most.

Checked everything else over on the Slash and all is well so I am at a loss.

[galland1]

Are you using LVC?

[ae rat]

at the very least one cell is toast.

[cLaWz]

No LVC on the XL5 ESC and none are compatible. Never ran it to where it lost power or for more then 5-6 minutes on the track.

[revo61]

I got 2 packs I raced twice a month, both less than a year old. They both are puffing. I was going to contact SMC Monday.