Hello!
I write this here, because I’m not sure whether this is an actual bug.
I like to work non-destructive, so I often use link objects to be able to change things later.
I recently mirrored a character using linked copies. But when it came to rigging, I thought I would have to create single-user copies. But I didn’t.
Because I found out, that the vertex groups are only linked, if they are called the same.
So for example:
I have Hand.L and Hand.R, which are linked copies.
If I just parent them with Empty Groups to the armature, it won’t work. They will both follow the same bones (after assigning the weights), because then the groups are linked as well.
But if I parent them separately and then create for each object only the vertex groups, that are needed, it will work. The meshes themselves stay linked, but the vertex groups don’t.
That’s a bit weird and I’m not sure whether this was intended. But I don’t want it to be removed, because it is pretty useful, if you know it.