Steps to reproduce:
For an existing article
Add a new edit, using account ABC
Add a new edit, using account XYZ
Use revision deletion to hide the account name from the edit made by ABC
Attempt to use rollback on the edit by XYZ
Expected result:
Possible to rollback, the hidden username is assumed to be someone else (to avoid leaking whether it was indeed the same user or not)
Actual result:
notvisiblerev - "The last revision by a different user has been deleted"
Even though its still possible to undo the edit, and only the editor associated with the last revision by a different user was deleted, not the revision text
See also: T358269: Rollback not working for revisions with a hidden username (when top revision has hidden username)