Not enough room on Time Machine hdd after restore.

Hi to all!

I did my first-time-ever wiping of my MBPro's hard drive and full re-install of Snow Leopard and restored with my Time Machine back up just a week ago. I was a little anxious because I didn't know what, if anything, might be left "unrestored" apart from of course folders that I'd set for Time Machine to ignore in the past. All went smoothly and I'm very happy with that aspect. My hard drive is cleaner and the computer runs quite a bit more smoothly now.

With all of that, though -- now that I've done a full system restore, my Time Machine is telling me that there's not enough room on my external drive to back up my main hard drive. It's as if (or actually is the case that) Time Machine isn't using the previous back-ups as something to build upon and it's trying to make a first full back-up of my main OS partition.

My OSX partition is 225gb with currently 25gb free, my Time Machine hdd is 300gb with 110gb free.
Before my restore, I would occasionally get messages saying that an old back-up needed to be deleted to make room, which was fine, but now it's the case that no back-up can follow through at all. My last restore point continues to be from the day before my hdd cleaning and re-install.

Right now it seems like my only option is to delete my previous back-up history and let it start anew, which would be annoying, or to move Time Machine to a larger hdd, which I suspect is unnecessary.

I'm not the most knowledgeable on the finer details of how Time Machine's back-ups work, but any help and kind explanation will be really greatly appreciated!

Thanks very much.

Hmm... So could anyone at least please tell me if this is normal behavior or not? I'm sure that at least some of you have done a complete restore with Time Machine backups before.

I did a restore so that my hard drive would be less fragmented and would run smoother. I liked having my TM backups that dated back to around September or earlier last year. Just because the most recent backup has helped and served its main purpose doesn't mean that I necessarily want to delete my old archives and start fresh.
This seems to be rather moot now though, because I see now that my last attempt at a backup just a couple of days ago did go ahead and overwrite my previous histories. So they do appear to be gone and I've started fresh anyway. It's not as disappointing as it could be -- the restore itself has been great and fine. I just don't see why it needed to delete my whole previous history.

It's slightly annoying but not a massive deal. Now I know to have at least twice (or a lot more) my current hdd space for time machine if I want to retain old backups after restoring.