**System Information**
Operating system: Linux (and others)
Graphics card: nVidia 1060
**Blender Version**
Broken: 2.9x
**Short description of error**
In Weight Paint mode:
If I lock some vertex groups and then Weights -> Smooth (or any operation that has adjustable values), things behave as expected. BUT, if I then try to alter the values the Properties popup window, the list of locked vertex groups changes (revert/undo?), which causes weights to bleed undesirably & defeating the purpose of locking groups.
This can sometimes even return a "All groups are locked" error, if the previous configuration had 1 or less groups unlocked and Weights -> Normalize All is performed, as Normalize All needs at least 2 groups unlocked to shift weights around and if you try to alter the properties popup it will revert the locked weights list to an incompatible configuration.
I've tested this with the Smooth, Levels and Normalize All procedures, and all reveal the bug. So I'm assuming this will affect any Weights operation that has an adjustable popup.
**Exact steps for others to reproduce the error**
1. Create cylinder (subdivisions not needed, but helps if you wan to understand the technique being used).
2. Skin cylinder to chain of at least 3 bones that resides within the cylinder.
3. Enter Weight Painting mode.
4. Lock all but 2 of the vertex groups, and select one of the unlocked groups.
5. Activate Weights -> Smooth
6. Adjust some values on the Factor or Iterations on the Properties popup.
7. Notice how the list of locked groups changes.
{F9532295}
**Assumed Issue**
Perhaps Blender is altering these Properties values via Undos?
If, in between steps 4 and 5, you perform another action (i.e. enter and exit Edit mode) it will not change the list of locked Vertex Groups.
**Importance**
This weight locking technique is very effective in preventing skin weights from bleeding across the model when skinning, causing messes that require cleanup (*see Demeter's tutorial on "[[ https://cloud.blender.org/training/weight-painting/5efe0d7405aef1cf3b89644d#comment-4576 | Weight Painting Part 2 ]]", at 9:30 where he demonstrates the problem and his workaround, which introduces other problems. In the comments of the tutorial, I demonstrate the precision of the locking weights technique and how it prevents bleeding, thus preventing the need of the destructive "Clean" operation.
This bug prevents the awesome property sliders from being used, meaning that values have to be set very low and the weighting operation needs to be performed in multiple steps till the desired effect is reached. This is not a very effective workaround.