1. Isn't that just due to the contract with Emilia? Maybe the contract with Subaru is different.
2. She was there to help at the mansion.
edit:
Oh btw, Roswal - present time, talks a bit like that Melancholy guy. During the scenes in the past, he didn't (or did he?).
You know, his "Eeeehhheeeeeeeeeeheee" or "Noooohooonii" thing he does at the end of a sentence.
Not to mention that the same guy looked a bit like a clown/jester, while Roswal looked like a normal noble more or less in the past and not like a jester at all, like he does now.
I'm smelling a connection.
What I can say with almost full certainty, is that he adopted his style and speech for whatever reason