CUSTOMTABLEBACKGROUND does not appear to work

[bttc]

I attempted to add the CUSTOMTABLEBACKGROUND definition as described in this post from 2011 http://www.lackeyccg.com/forum/index.php?topic=1300.0. I added a file Map.jpg to my images/background folder in the lackey root (where all the default backgrounds are stored), and added the following to my plugin:

<definition><kind>CUSTOMTABLEBACKGROUND</kind><value>Map.jpg</value></definition>

http://puu.sh/nGZYW/33a85f9665.jpg

As far as I can tell, it doesn't work--I tried using just <value>Map</value>, and it didn't help. I also tried making a \backgrounds folder inside of the plugin's images folder, and it was also a no-go.

Am I just missing something, or was this feature removed in the past 5 years?

Thanks!