A common problem seems to be that older transactions are added (by mistake) that change and invalidate balances in "other side" accounts. This may, for instance, happen because of (OFX) downloading transactions and automatically mis-classifying them.
It is very tedious to find such problems by going back and comparing balances with account statements.

My way to make this easier is to add empty transactions to my current account that contain a comment such as "BALANCE CHECKPOINT 21748.99", indicating that the balance on that date was 21748.99. If the balance is incorrect, one can then filter via the CHECKPOINT keyword and easily find the time span when the recorded balance was no longer correct.

I think that this sort of thing could be implemented as a feature in Moneydance. Add a reconciliation point transaction that records a "checkpoint balance" (and doesn't affect the balance at all). Then, whenever a balance in an account changes because of any event, the latest checkpoint is inspected. If it changes, the user is warned, and the event can be undone or canceled. It is easy to see that this feature is O(1) in time as only the latest checkpoint needs to be verified per account.

A good terminology for this might be to "freeze the balance", or to "add a balance checkpoint".