winbindd nsswitch fails with RID backend on 12.04

Thanks for reporting this bug. Marking confirmed due to upstream report. Marking high priority as there appears to be no workaround and it affects core functionality (login).

I am having the same problem: wbinfo -i $USER gives
failed to call wbcGetpwnam: WBC_ERR_DOMAIN_NOT_FOUND
Could not get info for user $USER

debug from winbindd -d10 -i
accepted socket 27
process_request: request fn INTERFACE_VERSION
[ 3500]: request interface version
winbind_client_response_written[3500:INTERFACE_VERSION]: delivered response to client
process_request: request fn WINBINDD_PRIV_PIPE_DIR
[ 3500]: request location of privileged pipe
winbind_client_response_written[3500:WINBINDD_PRIV_PIPE_DIR]: delivered response to client
process_request: Handling async request 3500:GETPWNAM
getpwnam xxxxxxxxx
     wbint_LookupName: struct wbint_LookupName
        in: struct wbint_LookupName
            domain : *
                domain : 'xxxxx'
            name : *
                name : 'xxxxxx'
            flags : 0x00000008 (8)
     wbint_LookupName: struct wbint_LookupName
        out: struct wbint_LookupName
            type : *
                type : SID_NAME_USER (1)
            sid : *
                sid : S-1-....
            result : NT_STATUS_OK
     wbint_QueryUser: struct wbint_QueryUser
        in: struct wbint_QueryUser
            sid : *
                sid : S-1-....
     wbint_QueryUser: struct wbint_QueryUser
        out: struct wbint_QueryUser
            info : *
                info: struct wbint_userinfo
                    acct_name : NULL
                    full_name : NULL
                    homedir : NULL
                    shell : NULL
                    primary_gid : 0x0000000000000000 (0)
                    user_sid : S-0-0
                    group_sid : S-0-0
            result : Time limit exceeded
Could not convert sid S-1-.....: Time limit exceeded
wb_request_done[3500:GETPWNAM]: Time limit exceeded
winbind_client_response_written[3500:GETPWNAM]: delivered response to client
closing socket 27, client exited
accepted socket 27
process_request: request fn INTERFACE_VERSION
[ 3502]: request interface version
winbind_client_response_written[3502:INTERFACE_VERSION]: delivered response to client
process_request: request fn WINBINDD_PRIV_PIPE_DIR
[ 3502]: request location of privileged pipe
winbind_client_response_written[3502:WINBINDD_PRIV_PIPE_DIR]: delivered response to client
closing socket 27, client exited

using Samba 4.0.7 (compiled by sernet, https://download.sernet.de/packages/samba/4.0/ username and password needed) solved partly the problem.
Another Bug report can be found on https://bugzilla.samba.org/show_bug.cgi?id=10062