msExchRequireAuthToSendTo attribute for the DL shows "not Set" instead of False

Strange situation.  

Exchange 2010 SP1 on Server 2008 R2 ENT

We are trying to allow Outside emails to be delivered to certain DL  In EMC we either unchecked "require that all senders are authenticated" or use exchange powershell to set this attribute to "false"

the issue = In active directory, the msExchRequireAuthToSendTo attribute for the DL shows "not Set" instead of False which causes mail not to be delivered.  We then have to change this attribute to False in ADUC r. (Our exchange admins have no access to this in ADUC.)  Any ideas why this is happening and the attribute is not showing Flase?

Thanks!