System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 970/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 457.09

Blender Version
Broken: version: 2.92.0 Alpha, branch: master, commit date: 2020-12-23 18:13, hash: rBc9efb5424079
Also broken: 2.90.1 , 2.91

Short description of error
If one changes the vertex group order at Object Data Properties it changes the groups that has been selected to the data tranfer modifier.

Exact steps for others to reproduce the error

From Default File

1. Create Armature.
2. Select Armature and go to edit mode.
3. Duplicate the Bone two times so that you have Bone, Bone.001 and Bone.002.
4. Parent (keep offset) Bone.001 to Bone.002.
5. Parent (keep offset) Bone.002 to Bone.
6. Parent the default Cube to Armature with automatic weights
7. Check Cubes Vertex Groups. You should now have the order from top to down: Bone, Bone.002, Bone.001
8. Duplicate the Cube.
9. Add data transfer modifier to Cube.001
10. Set ”Source” for the modifier. Set Cube as an source.
11. Select ”Vertex Data” form the modifier
12. Select ”Vertex Groups”
13. Set mapping as ”Topology”
14. Set Bone.002 to” Layer Selection”
15. Set Bone.002 to ”Layer Mapping”
16. Press ”Generate Data Layers” cause ritaul requires so.
17. Go to the Cube.001 ´s Object Data Properties and change the vertex group order by selecting ”Sort by Name”. The order should now be Bone, Bone.001, Bone.002.
18. Now go back to the modifier and see that the Layer Mapping section has changed from Bone.002 to Bone.001.
19. Select ”Cube” form the outliner or viewport
20. Go to Object Data Properties and change the vertex group order by selecting ”Sort by Name”
21. Select ”Cube.001”
22. Now go back to the modifier and see that the Layer Mapping section has changed from Bone.002 to Bone.001.

Ready made file

Expected result: Switching between Sort by Name and Sort by Bone Hieracry in the Object Data Properties should not have any affect to the selections in the modifier.