Yes, it is very strange with the Oathbreaker. It feels like an armored Warlock. Or in other words, if there is a mulitclassed Oathbreaker / Warlock later on, he feels like he has two Pact creatures he is bonded with. I don't know what to make of it.
This dilemma is spoken of by the Hound in GoT and ASIF and is one of the reasons he refuses to be a knight. It's also involved in Jaime Lannister getting the 'king slayer' epithet.
The Greeks had something similar. Orestes was the son of Agamemnon and Clytemnestra. Clytemnestra killed Agamemnon. Orestes is duty-bound to avenge his father yet also duty-bound to never harm his mother.
