RN 214 firmware 6.9.1 unable to find AD users starting with a number

we have joined the NAS to our AD (not cached localy as 80,000 users), and can add users to shares, however where the username starts with a number it will not search for or find the users . 

e.g. I add a user dt1t to networks RW access on a share , I see in /var/log/readynads/ads.log this entry

[17-12-19 14:28:09] 2143 rndb_ads_utils.c:176 info: ADS CMD::ldap search open: LANG=C net -P ads search \(\&\(objectClass=user\)\(\!\(sAMAccountType=805306369\)\)\(\!\(sAMAccountType=805306370\)\)\(sAMAccountName=dt1t\)\) sAMAccountName objectSid distinguishedName mail primaryGroupID memberOf cn

and the user appears in the list of those with RW access in the web interface, however if I add a user 1007111w (or any user starting with a number) this user never appears in the/var/log/readynasd/ads.log and disappears from the webinterface when you click apply.

the user info can be retrieved using 

# wbinfo -i 1007111W
1007111w:*:170546:33281::/home/CAMPUS/1007111w:/bin/false

if I put in non-existing users starting with letters or punctuation marks I can see the lookup in the ads.log, if I put anything starting with a number, it never looks up. 

WHY?