If the packets are sonically welded, it must be physical forces that are causing people's packets to come apart. It seems that with this particular tinder, protecting it in a container of some sort would be indicated.
I think I'm going to try to find a small container just for the tinder for my kit.
-john
Anything in foil in a pack is likely to get jostled, loosened, and leak... power bars, light sticks, even this wetfire tinder. It's the nature of the package.