I don't think that's what he meant. He is referring to the fact that the
keybinds and their relative positions do not change between specs, not even on Bartender. For instance, if you bind the "3" key to "Q" in your primary spec, then in your secondary spec, the "3" key must also be bound to "Q", and you can't make it anything different.
I don't know if there is an addon that addresses this, but I have sidestepped the issue by simply placing my buttons in their correct relative positions in each spec.