And the Clear! The thread you linked is about the Clear doing it. Amir also noted the issue in his Clear review as did Oratory1990 in his EQ for the Clear (pdf).

I think it's definitely something that effects the open backs rather than the closed backs, as Focal say in that statement. But it definitely affects the Clear as well, and in my experience, a bit more than the Utopia, I have to go a little louder on the Utopia to get it.