I think it is the lack of a merge function that is tripping you up. I suspect you are deleting the downloaded transaction.
Merge would combine the two transactions into one thus resolving the problem but without it you should probably be deleting the manually entered transaction. Download transaction, when using the OFX protocol, have a unique transaction ID in them. This is what Moneydance uses to determine if it is a duplicate or not, if you delete the downloaded transaction then you do not have a transaction with the ID in your register hence it will be downloaded and entered again, there is no way of entering the ID into a manually entered transaction.
Thanks for the suggestion. I'm pretty sure that's what I did in 2018 when I originally downloaded the transaction. Looking at the details for the transaction that was cleared a year ago, it has ID information and original description that are similar to the newly downloaded transactions. That is to say I've already downloaded this transaction and merged it with the manual entry a year ago. The new transaction won't offer to merge with the existing transaction even though the amount and date match.
Coupled with the fact that I know this account hasn't been unconfirmed for a year, I'm pretty sure somehow USAA re-queued these transactions in the last month or so when I started to notice the issue. I'll just leave the zeroed-out transactions in place so that they don't keep downloading over and over.
There have been cases of Financial institutions redoing systems and assigning new transaction IDs to existing transactions so it is not beyond the realms of possibilities that USAA has done something like this.
Alas there is not much that the software can really do about this. In the case of Moneydance about all they could do is extend the merge capability to Investment accounts so you could deal with the issue if it happens.
Heh, I closed this discussion and opened MD, only to find even more transactions from May 2018 that are popping up in other USAA investment accounts. They appear to be having trouble with their system.
Just for documentation's sake, USAA is continuing to offer new transactions from May 2018. For reference, the accounts that keep doing this are managed accounts with multiple securities. When I started re-using MD in 2018 (after a multi-year hiatus), I hand-entered all of the transactions that didn't initially download so that my account balances were correct. Now I have to go back and delete the hand-entered transaction. Otherwise, in my experience, the downloaded transaction will keep downloading.
It's a little more frustrating for my older accounts that were so old I didn't have access to all the previous transactions. For those I entered everything that was available to me at the time and then made a bunch of dummy purchases to make the balances work out. For these accounts, each time USAA throws some new data at me I have to alter those dummy purchases or the portfolio values will be incorrect. I figure by 2025 all of May 2018 will finally finish downloading :-)