I posted this in the VEF netwings forum ~
http://www.netwings.org/dcforum/DCForumID38/2005.html#5
It seems that it's not a bug, just a sneaky German 'dummy' train located close to the real target to encourage us to waste our ammo. We should have noticed really that it didn't have any AAA or an engine attached.
This makes sense as the target we were supposed to be a attacking was a depot - usually a bunch of vehicles parked up in a field. For some reason we got fixated on the train station and this dummy train.
Oh well - lesson learned.