That normally happens, if the modder has not setup the mirror meshes properly. They need to be splitted into single meshes for each mirror, that have to be named properly, use the name 'mirror' as the name for the used material and put into the cockpit instance.
It's not just 1 file and you'll have to use a software like 3dsimed3, to set everything properly. Are you familiar with that? The best way, is to contact the developers of the mod and ask them for a fix, to get it working for all people that use the mod. .