Function wbcGetgrlist(declared in nsswitch/libwbclient/wbclient.h) returns an empty group list.
Here is the description of the function:
* @brief Return the next struct group* entry from the pwent iterator
* This is similar to #wbcGetgrent, just that the member list is empty
* @param **grp Pointer to resulting struct group* from the query.
* @return #wbcErr
wbcErr wbcGetgrlist(struct group **grp);
However, in nsswitch/winbind_struct_protocol.h, the corresponding implement is:
/* this is like GETGRENT but gives an empty group list */