[Samba] question about winbind rid idmaping

[Andrea Cucciarre']

Hello,

I have just realized that winbind rid idmapping create the following 
idmapping for user, below an example:

# id HYPERFILE\\simone
*uid=11663*(HYPERFILE\simone) gid=10513(HYPERFILE\domain users) 
groups=10513(HYPERFILE\domain 
users),*11663*(HYPERFILE\simone),3011(BUILTIN\users)

I'm confused about group mapping 11663(HYPERFILE\simone), winbind 
created a mapping for a group that has same name and id as the user, 
although such group doesn't exist in my AD domain.
This is causing issue in the ACL module that we are developing.
Does anybody know why winbind behave that way?

Thanks
Andrea