I had one when I was a kid, I got a 1/25 scale 1950 Ford coupe as a gift the body was so warped that I could not do anything with it. I neatly put all of the parts back in the box, set the box in the middle of the floor and jumped up and down on it several times.
I mixed some car body repair filler a few days ago, slapped it on the underside of my Seaview's front end, came back a couple of days later and it was still soft... looks like I didn't put enough hardener in it :-(
Just scraped it all off again a while ago with a knife, came right off with no effort at all!
Not a model exactly but while working on my Martian diorama yesterday I found out the box of Marblex clay I'd bought some 6 months or so ago to make a mountain range in the distance had dried out while still in the package. I'd never used the stuff before so didn't realize it has a limited shelf life. Anyway, I almost threw it out but then realized I could still chip chunks off the block and use them for boulders in my Marscape. It might even work better this way. Lemons into lemonade.