user supplied default-user-image does not display properly in lightdm-gtk-greeter

Version: Xubuntu 14.04
Environment: Corporate install joined to MS Windows Active Directory using PBIS Open 8.0.0.2016
default-user-image specified in /etc/lightdm/lightdm-gtk-greeter.conf

Expected behavior: Specified default-user-image replaces the noname-user graphic in login dialogue in every configuration.

Experienced behavior: works as expected unless "greeter-hide-users=true" is specified in /etc/lightdm/lightdm.conf. When "greeter-hide-users=true" is specified, dialogue reverts to the noname-user graphic and ignores default-user-image.

In our environment, there is only one user account on the local machine, used for administrative purposes. All other logins are authenticated with AD credentials and AD usernames do not appear in the local user list. we must use the Manual Login option to allow AD logins. As a mild security measure, we'd prefer that the local admin account name not be displayed to users, so we need to hide usernames. There are workarounds to remove the local admin account from the user list, but the result is a pulldown saying "Other..." which gives the installation the look and feel of a non-professional hack job.

Am I missing something here, is this behavior intentional, or it it a bug?

D.