I made a jack o lantern with my gf a few days ago and now it has like melted. It's flattened out and oozing out the bottom. Kinda looks cool, but its nasty. In the past I've had jack o lanterns last up to two weeks. Never seen this happen before. I guess they sold us a faulty pumpkin.
Same thing happened to me. Did you keep them inside? I think that is where we went wrong. My theory is that the temperture is perfect indoors for mold growth.
I usually put my jack o lanterns in a big bucket of cold water for a couple of hours, if the temps are warmer. Keeps them fresh a bit longer.
This year, the temps are in the mid 60s-70s, and humid - rain every other day - so I tried another method I read about. Sprayed the cut surfaces and inside of each with clorox clean up spray. It's supposed to keep bugs and ick at bay. The one pumpkin which we carved earlier this week (exposed brains) is still looking good. I gave it another quick spray when I put out the others yesterday, but it didn't have the usual column of ants wandering through it, so I think it's working.