This is very common and has to do with fat density. Full fat cells will push out the skin and you can feel pretty firm. In fact they can be so compacted in a given area you might even think it is muscle - for example a person might think they have big muscular calves only to find out that after losing 100 lbs they had a whole lot of fat in those calves.
You lose fat - the density goes down - the area becomes softer and "giggly". I always thought it was jiggly though...
I've just had an "ah-ha" moment thanks to this post. I realize why I've been so "down" lately and it's because I'm getting JIGGLY! It is making me feel like "what the @##$ is going on?" because I 'feel' fatter than I was before because my fat was 'firmer'.... I think now that I've read all these posts, I understand a bit better that the jiggles are aGOOD thing and I'm gonna be embracing my jelly belly instead of feeling frustrated about it! Thanks for posting your question -- you answered one I didn't even know I had!