trouble just starting reconciliation

[hendrik at topoi.pooq.com]

I'm running gnucash 1.8.10, the version that is distributed with Debian 
sarge.  I' having trouble with reconciliation of my chequing account.

Specifically, when I *start* reconciling, before I've checked *any* 
transactions, the starting balance is different from the reconciled 
balance.

How is that possible?  I thought they were both initialized to the sum 
of all reconciled transactions so far, and that subsequently, the 
reconciled balance would change when you checked off transactions and 
the check-marks appeared in the 'R' columns?

Please, tell me how these things *are* computed, so that I can start to 
track down the discrepancy.

And I am capable of hand-editing XML files, if that should end up being 
necessary (though I haven't done it yet, so that shouldn't be the 
trouble).

-- hendrik