OK, I have now been able to reproduce this as well.
I believe this is caused by the following two conditions:
- At least two hidden fields with the same name.
- The field value must differ.
If I were to guess the root cause, it would be that Bitwarden includes some code to check whether a hidden item has changed (i.e., it has changed its name or its value) when the item is saved. If it detects a change, then it updates the password history. I believe that this code is getting confused when the above conditions exist.
Edited to add: The root cause seems to be that the database structure for custom fields does not include unique identifier for the fields that are created, so they are identified only by their name & type. The same problem causes the “Updated” timestamp to be erroneously modified by a Edit/Save sequence if two non-hidden text fields have the same name but different values (even when no modifications were made).
In my opinion, this is a bug, and should be reported on GitHub. Good find, @Timmy256!