Disclaimer: I Do Not Own Harry Potter.
She leaves her clothes on the floor of his bedroom and it irritates him which is probably why she does it.
All that matters to her is getting a reaction from him whether its positive and negative.
If he ignores her she does something like kill a death eatee thats useful to him or makes sure mission is a failure just ensure he has no choice but to acknowledge her.
So ignoring Bellatrix was never an option for him.