Steps to reproduce:

1. Find a release group with ≥ 2 releases, where the title of the RG and the two releases need to be updated (e.g., changing ASCII apostrophes to appropriate Unicode punctuation).
2. Open the release editor for both releases in separate tabs.
3. Correct the title of the first release, check the “Copy the release title…” checkbox, and submit the edits.
4. Switch to the other release, correct its title and check the “Copy…” checkbox again. The edit summary now doesn't show the RG edit anymore, since the name of the RG is already the same as what would be copied.
5. Submit the edits for the second release. The submission never finishes, and the only way to fix this is to reload the release editor entirely.

Traceback in the console:

Uncaught TypeError: can't access property "edit_type", t[0] is undefined
    callback edits.js:609
    i edits.js:563
    jQuery 2
    jqXHR request.js:19
    jQuery 6
    c request.js:16
    default request.js:37
    x edit.js:469
    i edits.js:558
    submitEdits edits.js:578
    submitEdits edits.js:717
    init knockout-delegatedEvents.js:71
    jQuery 2
    r helpers.js:71

FF 90.0a1, userscripts disabled, although I don't believe this is browser-specific. Happens both on beta and prod.