System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 456.71

Blender Version
Broken: version: 2.93.0 Alpha, branch: master, commit date: 2021-03-31 07:46, hash: rB645fc0c76794

Short description of error
have vcol "A" (with "a" written)
have vcol "B" (with "b" written)
If we create a geonode modifier and do A + [0,0,0] = A with a vector attr math node,
blender is somehow replacing "A" with "B" which is really strange.
so there's a vertex-color mismatch going on, and the attr is not being written correctly in vertex color layers

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