Time Machine repeatedly does full backups, including FileVault while logged in

Question

So let me preface this - for months I'd hoped for a way that Time Machine could backup my FileVault encrypted account without logging out.  Last night Snow Leopard spontaneously started doing this.  I know many may think that I'm looking a gift horse in the mouth, but read further and hopefully someone can help me make sense of this.
Last night I attached my external 1TB USB hard drove to my 15" MBP (spring 2010 model) running OS X 10.6.7.  It started doing a Time Machine backup automatically, as usual.  Since I was logged into my account that uses FileVault (a massive home folder - 220GB) I expected a fast backup of things only outside my home folder.  As i looked at the details, however, i quickly realized that it was backing up all 270GB of data on my hard drive - including my FileVault account while still logged in! 
At first i thought i just got lucky - i'd been craving this feature for years and it just happened to me without even doing anything.  Curious guy that i am, i logged out of my acct with my USB drive still attached to see what would happen.  After FileVault cleared out space in my home folder, it did _another_ backup, that took about 10 minutes to complete.  This seemed strange so i logged back in and started another backup manually.  To my utter shock, it started doing the whole 270GB over again! 
I even cleared out my TM drive, erased, reformatted, checked permissions, etc etc and did the same on my system drive, hoping that it was just a matter of broken permissions.  No change.
So there's two things going on here and i'm pretty concerned about both:
1) Why is TM backing up my entire encrypted home folder while i'm still logged in??? Apple has clearly designed TM and FV to NOT work this way for data integrity reasons and the fact that it's happening has me freaked out a bit over the reliability of my backups.
2) Why is TM doing full backups after each time i login to my account?  If i stay logged in, it appears to only do incremental (normal) backups but if i logout, then re-login and allow the hour to pass and let a backup start on its own, it starts the whole 270GB again.
I'm getting to the point of wiping the system and starting from scratch but since i presently live in a country with no Apple store and extremely poor internet access, that prospect horrifies me
any ideas?
many thanks,
-Tim

Answer 1

Thanks for the input Pondini -
I tried deleting the file as mentioned in #A4 and it still had the problem.  Last weekend i finally got a brand new hard drive and reinstalled OSX 10.6.3 from scratch, then promptly applied the 10.6.7 combo update.  I purposely chose to NOT import my old user from backup and instead set up everything again manually (royal pain, but the only way i could be sure that i wouldn't bring the problem with me).  Today i whipped out my TimeMachine drive and set it up for backups.  I crossed my fingers and it AGAIN started backing up all 250+GB of my system from within my FileVault protected account. 
My wife's MBP is still running 10.6.4 and i'm beginning to wonder if his is an issue with 10.6.7 since i'm relatively certain i didn't experience this before that upgrade. 
I've checked my wife's exclusions under Options and her home folder is NOT in that list, yet her TM is not attempting to backup everything until she logs out of her FV acct.
In response to Linc Davis, _yes_ it was backing up my info into a sparsebundle file, not just the raw unencrypted data, which is extremely strange.
If i DO add my home folder to the exclude list, will it still be backed up when i log out?
At this point, i'm thinking my next steps are:
1) try a different TM backup drive, even though i've wiped and checked my current drive numerous times
2) downgrade to an older version of Snow Leopard to see if 10.6.7 is the culprit
Any other ideas?