Thats terrible mate. I can only assume that its what everyone says, just a bad batch.
The other week i was fishing with the same stuff and the water temp was quite cold, i made a stick up and threw it in the margins where i could see how long it melted. It took 4 mins before it started to dissolve and within 7 minutes it was all gone.
Just a bit of completely useless information there but it gives everyone a rough guide to how long the stuff takes to melt.