I don't understand how "balance" is computed

I have an account with all entries reconciled [I 'm pretty sure -- I wish
you could limit a search to a single account!] and a balance of -300.00.
The account balance was supposed to be zero .   So I deleted one 300 dollar
payment...  and the balance didn't change.

why didn't deleting the transaction  change the balance??? [i tried
changing it from reconciled to cleared to uncleared to voiding it and
deleting it and the -300 balance didn't change].

BUT: if I create a fake deposit of $300, that *did* zero out the account. 
So I don't understand quite what the "balance" is telling me, because I
would have guessed that deleting a payment was the equivalent of adding a
deposit but there's something odd going one: if I add a new payment or
deposit the balance changes appropriately... but if I change or delete an
old payment or deposit it doesn't.  What am I missing?

  /Bernie\
-- 
Bernie Cosell                     Fantasy Farm Fibers
[email protected]            Pearisburg, VA
    -->  Too many people, too few sheep  <--