zcash_client_sqlite: account_balance_delta is non-deterministically set to *balance* at the time instead of the delta

[AArnott]

I have access to a Zcash account of one of my users, where one particular transaction will sometimes be downloaded and reported in the v_transactions view with an account_balance_delta of the new balance on the account after the transaction is applied instead of the delta that led to that balance.

Ya, pretty weird.

Specifically in the bug repro case, it is set to 81726753. In the "good" case, it is set to -285674820. In both cases, the data in the database expresses that the transaction has one spend, a fee, and no incoming value. The spent value is 28566482, which when added to the 10000 fee equals the real delta on the account balance.
So why would that column sporadically be set not to the delta, but to the balance after the delta is applied?

This was a fully shielded transaction, BTW. So I don't think the explanation could have anything to do with UTXOs that had or had not yet been saved to the database.