You bet I'm doing the same thing. I feel like I'm not using my leg strength/power at all in my jumps. I just raise the chest and "jump" which is as retarded as it gets. I know it doesn't look like that in my videos but living in my own body (weirdly enough) I can tell you that's true.
The thing is - how do you correct it? That's why I liked a lot what Rippetoe said about the low bar hip-driven squat. When I heard him say "don't drive the chest up, use your hips" for the first time, I was like "bingo, that's what I have been doing all along".
Now don't live under the impression that I was "manipulated" into thinking that - I know I have always "raised my chest" but it never occured to me how to put it into words.
The problem is - I have no idea how to cure it.
When I deadlift I raise the chest.
When I clean I raise the chest.
When I squat I don't though, weirdly enough. I put a lot of quad load instead (I don't really push my hips back because I'd just fall backwards)
When I KB swing I can use my hips pretty well.
When I RDL I raise the chest. I feel the same tendency to fall on the back when I RDL as in the squat (or even more really) - it's really, REALLY annoying.
Any ideas on how to fix this? Box squatting could be an answer but I don't have any boxes in the gym and using a bench that's very narrow I could easily miss it and just have a big accident happen. In fact, because of my fear of missing the bench, when I was doing "bench squats" I was even more quad dominant than in a free squat.
So as you can see, I'm a really weird kind of guy. But hey, you already knew that didn't you?