I seem to remember that this was logged as a feature suggestion some time ago.
The reason I read, and I believe it to be valid, is that the HPF is part of the input circuitry of the mixer, not the EQ section. In my opinion, an HPF should not be considered EQ. It is to remove unwanted low frequency audio whereas EQ enhances what is already there. In saying that I still look for the HPF control in the EQ section so maybe that indicates that the control belongs there.