A couple of days ago I was messing around with the TTL meter on my Minolta X-700 and my hand held meter in order to conduct a film test sequence. The sequence called for the use of a piece of black card stock instead of an 18% grey card because a reflective meter would read the black card as 18%.
Wanting to see if it was really true, I set my black card in an evenly lit spot in the shade, and then filled the viewfinder, set it on infinity and took the reading. I also took a reading with my hand-held meter. I next took away the black card and placed a Kodak grey card in precisely the same spot and at the same angle. I came up with one full stop difference in the readings between the grey card and the black card, and with both my TTL and hand-held meters.

Does someone have and idea as to why this might have happened? Shouldn't the TTL and hand-held meters have been 'fooled' into reading the black card at the same value a grey card?

I'm confused