It's a little confusing, but like rustyspoons said, it doesn't get the negative.
Basically a weapon like the katana is both 1H AND 2H at the same time, the way your character uses it is just dependent on whether you have a shield or are riding. Think of it as 50% 2H 50% 1H
Langes Messer is EITHER 1H OR 2H depending on the mode you use, so no penalty either way. Think of this as being able to swap between 100% 2H mode or 100% 1H mode.