That my be the source of the problem, I have been told it doesn't matter if you chose the wrong faction.
I have been able to use american AP rounds on my AT when I have chosed britz in the lobby and britz can't use AP if they cap a AT?
Its true, you can't build buildings and use some abilities if you select the wrong faction.
weird I have been testing this extensively recently with my artillery tree..
I guess it really enables somethings and disables others.
I wonder if the pak cloak thing is tied directly to being wehrmacht, it must be. Most other abilities aren't.