Mapping Windows groups to uids (with idmap and rid)

[Assar]

I discovered that in Windows, files can be owned by a group that this
is not supported by Samba (3.2.3).  In my case, I'm using idmap and
rid.

How can these Windows groups be mapped to uids?

If my limited understanding is correct, the mapping that you have are:
(with idmap and rid - perhaps this is not the case in general?)

Windows group: SID=s0, RID=r0          <-   -> gid_t = g0 = f(r0)
Windows user:  SID=s1, RID=r1          <-   -> uid_t = u1 = f(r1)

And if I understand this correctly, the RID namespace is global, so
there can never be a windows group and user with the same RID?

If that's the case, what's to stop us from defining a mapping:

Windows group: SID=s0, RID=r0           <- -> uid_t = u0 = g0 = f(r0) 

If the RID namespace is the same, there should not exist a user with
RID=r0 and this mapping would be unambiguous?

I would appreciate any feedback on understanding this problem and what
can be done to make this work. 

/assar