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Bone Constraints disappear after Undo
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Description

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 1060 6GB/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 452.06

Blender Version
Broken: version: 2.83.5, branch: master, commit date: 2020-08-19 06:07, hash: rBc2b144df395f
(I also tested in 2.9 beta, with the same result)
Worked: I don't know if it worked in earlier versions

Short description of error
Bone Constraints disappear after Undo. Specifically when you delete symmetrical bones with the "X-Axis Mirror" option ON, and then press Ctrl+Z.

Exact steps for others to reproduce the error

  1. Create a new single bone
  2. In Edit Mode, rename the bone to "Bone.L", move it a bit in the X-axis, and duplicate it.
  3. Constrain one bone to the other with any constraint, say "Copy Rotation"
  4. Symmetrize both bones. Now one bone on the left and one on the right has a Constraint.
  5. In Edit Mode activate the X-Axis Mirror option.

File in step 5:

  1. Delete Bone.R with Constraint on it.
  2. Press Ctrl+Z (which is very common because often you only want to delete the bone on one side but X-Axis Mirror will delete it on both sides).
  3. Go to Pose Mode and the Constraints on both sides should be missing.

If you keep pressing undo you can get to a state where the Constraints are applied. But if you keep working from step 8 above without realizing that the constraints have disappeared, then you may be unpleasantly surprised later on. I don't know if this can be explained with some features of the undo system. But it's definitely a bad user experience.

Event Timeline

@Germano Cavalcante (mano-wii)
I reported this some time ago but I didn't have the exact steps to reproduce the bug so you closed it as invalid. Now I do. Please take a look.

Todor Nikolov (ToshiCG) updated the task description. (Show Details)
Todor Nikolov (ToshiCG) updated the task description. (Show Details)
Richard Antalik (ISS) changed the task status from Needs Triage to Confirmed.Sep 2 2020, 9:32 PM
Richard Antalik (ISS) updated the task description. (Show Details)

Actually this has been already reported in T74486 and merged to T50423 so I will do the same.

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