The 19-year-old received positive comments from the panel for her performance of Prince's 'Purple Rain' on tonight's show, but Contostavlos also took the opportunity to address reports of her "mean" behaviour backstage.
"You are definitely a star of the show," she started. "But I think you're very competitive and I've seen a different side of you backstage. I think you don't realise that you do it, but in some ways you being so feisty can come off as quite mean to other contestants and I've been told that there's been mean comments towards them.
"I'm not putting you down, I'm saying take that feistiness and energy and bring it on the stage. When you get offstage, leave the war behind. Because I think you're going to be amazing, just put aside the attitude."
Gary Barlow, however, condemned Contostavlos's outburst, saying: "First and foremost, I'm here to judge what I see tonight. I don't care what goes on backstage, we shouldn't be getting involved in that."
Misha's mentor Kelly Rowland also urged Contostavlos to "leave things backstage", before announcing that she was "proud" of her act's performance.
The Destiny's Child singer then took exception to Walsh's suggestion that Misha had become overconfident, telling him: "I think that some of your category should actually get some confidence."
"One of my contestants has complained to me about Misha bullying them backstage," Walsh angrily responded, sparking a heated bickering match between him and Rowland as Dermot O'Leary asked Contostavlos to justify her earlier comments.
"At the end of the day, [The X Factor] is about a package and it is about character and when it is affecting other contestants, I'm sorry, I'm going to say something," she said.
Speaking on The Xtra Factor, Rowland again argued that Misha's behaviour should not have been scrutinised without judges knowing all the facts.
Contostavlos remained defiant though, declaring: "If she's going to make a bitchy comment to one of my acts backstage, I'm going to express it."
The X Factor continues tomorrow at 8pm on ITV1.
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