Insurgent Pickup Custom and AA Trailer?

I seem to be having an issue getting the AA trailer to actually hitch to my Insurgent Pickup Custom.

If I order the AA trailer it spawns with the normal pickup... but if I request my insurgent pickup custom the AA trailer disappears.

I can still order my "normal" insurgent pickup from Pegasus and the AA trailer won't disappear... but the custom and AA trailer don't seem to get along...

Am I missing something obvious?