Maybe I think differently - to me if it uses all the white notes, it uses all the white notes, you just play them in a different order to give a different effect. Yes, I know this is not the convention of nomenclature.

Another area of confusion is touched upon above (and we did eventually nail it down a long time ago on a different thread) is the distinction between "D dorian" - ie the dorian scale starting on D - and another dorian - the dorian that uses the notes of the scale of D major. I would express this by calling "D dorian" "the dorian OF C" but I think that others use a different convention.

None of which gets any closer to the fact or reason why the notes going up the melodic minor are different to the notes coming down the melodic minor.