Step to reproduce:
- Setup two gameObject (go1 and go2) with a component using MaskField. Be sure the MaskField could have 3 or more different mask. (MeshRenderer should use it for RenderingLayerMask with enough different masks).
- Set the MaskField with first field f1 on go1 in Inspector.
- Set the MaskField with second field f2 on go2 in Inspector.
- Select both go1 and go2 (see that the mixed value state is applied).
- Edit the mask field by selecting third field f3 (note that the mixed value state disappeared which is certainly an issue too regarding what we could attend from this).

What we is expected:
- go1 should have the masks f1 and f3
- go2 should have the masks f2 and f3

What can be seen:
- Both go1 and go2 have the same value. This seams to depend in what order go1 and go2 have been selected.

Note:
As a user, I expect each mask on the field to react like a checkbox. This means that if I multi-edit a mask on the field that:
- is active on only a part of the selected object, all selected should have it set to active.
- is active on all selected object, all selected should have it set to not active.
- is not active on all selected object, all selected should have it set to active.

Also, I'm pretty sure this could be more clear if the mixed value state (or not) was displayed in front of each mask when opening the dropdown. This in addition to have it on the selected one area as now.