I am resurrecting the closed discussion below. The problem still exists in at the end of 2025. Editing the duplicate transaction will corrupt the hidden transaction. The work around is to move to a different register and return to the original register. I showed this bug to a Quicken agent on 9/25/2025 Ticket #11968422.
While this bug does not seem to corrupt the hidden transaction unless the duplicate transaction is modified and saved. When attempting to enter the category into the duplicate, the hidden transaction category will be briefly visible. If changed, avoid changing the transaction by moving to another transaction and choosing "No" to the "Save" question.
This kind of bug undermines the credibility of the Quicken user interface and may corrupt the register if the user modifies the duplicate transaction and does not notice any inconsistencies when the transaction is saved.
I have screen shots but cannot display them in a public forum.
Editing a Transaction causes it to be duplicated and overrides the next transaction — Quicken