I don't really agree. She's the one who said blue could touch her bust in the first place and she was the one who said they could do that stuff again in chapter 6.
We've seen her step on blues foot, tell her she'll kill her, ask her if she wants to die, punch her in the face etc. She takes no shit from blue. It's surprising to see her so docile with the guy but I guess we'll find out what causes the change.
My guess is the flashback will continue at least until we find out why blue was crying down the phone on the bench and brown was calling her insincere.
Been trying to avoid longer comments but here I go:
She has her moments, I'd agree. But when it comes to the important issues, like romance, I'd argue she is still the same; and that's more what I was referring to. But that's not as important.
As for her "change." In the past we're shown, she's going through an abusive relationship, so how she acts while with her old boyfriend isn't necessarily indicative of her character back then, I'd say. The few moments away from him (like in chapter 22 during their gaming sessions) when we see her in a less toxic environment, she argues just like in the present and acts the same as her present self.
I don't think she's changed, moreso she was being harmed by who she was with at the time (and that person is gone now). She was diminutive around him and about him specifically. That relationship seemed to be the alteration to her normal personality, like those kinds of relationships can be. That would also make it even clearer why Blue does not want her to see him again and revert.
That's honestly what seems to be frustrating Blue in these flashbacks (besides romantic stuff). Blue probably couldn't understand why Brown would act so weak around this guy and hang around him. It can feel like the person you know has a split personality.
Similarly, in the present (to kind of go back to my earlier comment), though Brown can be forward about some things, it seems she's still reserved and cautious when it comes to being honest about her (apparent) romantic feelings for Blue. The bust stuff is a deflection, it's like play but she hasn't sent clear messages to Blue yet, when she's had plenty opportunity to tell her if she wants her exclusively (though it's still possible Brown doesn't consider herself "lesbian or bisexual" yet and that might be part of the reason).