Yea, haha. That's just an OOB thing. The game doesn't actually have a way to have one officer have multiple commands, so for officers that do, you need one for each level of command.(In this case one representing him as an army commander and one representing that he also commanded the 3rd corps)
Its one of those abstractions we talked about. Just think of them both as Wellington, one representing his army command, and one representing his corps command.