It never happened to me in therapy, actually..not that I can remember. I was hurt in therapy in various ways, but not in this way.

I never, actually, needed a T to be on "my side" so to speak. I didn't think it was their role to be my defender. I needed them to acknowledge abusive actions towards me for what they were, which they did for the most part. Other than that I saw their role as someone who can help me understand my own responses, desires, motivations and needs in relationships with other people. I was in therapy to understand myself better, not to get a paid friend who'd be "on my side" or an advocate.

I did need empathy but that is not the same as "taking sides" or identifying with anyone in my stories, myself included. Empathy is a deep understanding of someone else's subjective experience and perspective. As such, it is also different from support. Support is more like "I feel for you..I approve your choices..I have the same perspective on such and such issue". It may feel like someone's being on your side, but it's not exactly the same..

When people take sides, they forgo objectivity, which is not necessarily a bad thing in close relationships, but not in therapy. When I felt supported by my therapists, it didn't feel like they were taking my side or identified with me. It felt like my perspective on the situation was valid to them and that my choice, in their opinion, were the right choice to make in that situation. It didn't feel like they were "against" the other person in my story. The other person just didn't matter that much because therapy was about me and what I do in my relationships with others, not about what others do to me.

Conversely, my Ts never took the "side" of the other person, because, again, the other person was not the focus of therapy and, in that sense, they didn't matter. Sometimes, they did tell me what the other person's perspective might have been, but it didn't feel at all like they were defending them. It was, actually, more for the purpose of letting me know that I didn't need to take their behavior personally because they were acting out their own issues, as opposed to doing something "to me".

So, no, I was fortunate to have Ts, who acted professionally in that area..except maybe the last one..He was, as I remember now, trying to be my "knight on the white horse" who eagerly wanted to defend me from the whole world. It felt good on some level, but it also felt wrong, so I'd often let him know politely that I wasn't interested in wasting my sessions time on trashing other people, even those who hurt me a lot. I wanted to focus on my own emotions and to learn how to manage them better.