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Issue ID




Prefabs and Undo leads to crash



Reproduction steps:

1. Open ""
2. Open the "Main" Scene
3. Drag and Drop "Prefab A" from the Project window onto the child("Prefab B") of "Prefab A" in the Hierarchy window
4. Repeat dropping the "Prefab A" on the Last child ("Prefab B") 2 times
5. Click on the Second "Prefab A" and Click "Apply" in the Inspector window
6. Repeat dropping the "Prefab A" on the Last child ("Prefab B") 1 time
7. Click on the last "Prefab A" and Click "Apply" in the Inspector window
8. Click on the first child "Prefab A" and Click "Apply" in the Inspector window
9. Press "Ctrl" + "Z" ("Cmd" for Mac) repeatedly until the Editor freezes/crashes

Expected Result: The Undo function should Undo the actions
Actual Result: Editor freezes/crashes, sometimes just creates more prefabs outside of the main prefab with the child objects

Reproduced with: 2017.2.0b3, 2017.1.0p1, 5.6.2p4, 5.5.4p2

Notice how after step 5 the prefab in the Project window didn't update with the newly added child objects
Notice how after step 5 and step 7, upon clicking the "Apply" button, the prefab closes and when expanded there is one more "Prefab A" added

  1. Response avatar

    Resolution Note:

    This particular case has been investigated thoroughly and we have decided, in the interests of protecting the stability and features of Unity for users that rely upon the affected versions, to not address this fix for the time being. We understand that this will cause problems for some users, and so may address in a future version.

Comments (5)

  1. Ec2c3cd0ac70c37e1e2c0b3b93619f73?d=mm


    Jun 22, 2021 03:53

    Virtually everything in my game is a prefab, and I suspect the same is true of most Unity users, because that's more or less the correct way to develop. There is no point in having an undo feature if it behaves like this.

  2. 36c65e3934745df83910152c6a077e4a?d=mm


    Aug 18, 2020 04:59

    good one <a href="">lyricsauto</a>

  3. F0a3bb83ad222e04dc7750bfc671816f?d=mm


    Dec 31, 2017 19:15

    I've seen this around for a while, mostly ignored it till it happened several times in a row working on particle systems and prefabs.

    For me It seems to only happen when you delete and object on a prefab then undo it after making several new steps.

  4. 3a11f6892a451063b7979225e4c9b257?d=mm


    Nov 09, 2017 16:43

    In 5.6.0f3, I got this after only adding a text component to a prefab and hitting Ctrl+Z. I hadn't even applied the change. All it took was those two steps.

  5. 9b9d6b7b7be4d68f7b033c8955c2f4bc?d=mm


    Aug 17, 2017 09:35

    This just happened to me in 5.6.2p4: I changed a prefab, applied the changes, then started undoing. Crash.

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