when you make a bar a possess bar in macaroon it shows as is for the current state you are in. Ie as a possess bar when you are not a zombie or mounted etc it will show what you would see in your "normal" state. when you do become "possessed it switched state and you have to configure the bar at that point for the Possess state.

ex:
you make bar 1 your main AB and also your posess bar.
Un posessed or in your normal combat or non combat state the bar shows bar 1
when you mount, become a zombie, do the frost wyrm mission for starter DKs your bar changes to a different version of bar 1 and you must then configure the bar as normal.
so mount up > bar edit > add buttons to your posess bar as normal.

i hope this makes sense. i figured this out the hard way when doing the DK quest.