Time Machine Question

This afternoon, I had a little mishap (Somehow pairing with a Bluetooth headset completely hosed my Leopard installation, past the point where a reboot fixed it. I won't try that again) so I had to restore from Time Machine. Which, BTW, is an awesome feature. Popped in my Leopard DVD, told it to restore a backup from earlier this morning from my Time Machine disk, left to run some errands while it did it's thing, came back, and after a quick reboot, my system was back to where it was this morning when everything was working great. Seriously folks, if you aren't using Time Machine, go out and buy an external hard drive. It's awesome and truly a life saver. If I didn't have Time Machine, I'd be spending the rest of the weekend backing up, doing a fresh install, and then restoring my junk and reinstalling my apps.

Anyways, now that I'm back, it looks like Time Machine is creating a full backup now, taking about another 50 gigs of space on my drive. Anyone know why this is? I would've assumed that after I restored my system, it would just continue operating like normal...only backing up what's changed in the past hour. Thanks