Q: Smart group "is member of" works different than expected

Hi

I would like to find out which address cards are not in group a and in group b at the same time.

That's why I created a smart group like:

- card is member of group a (eg. Daylite) (and)

- card is not member of group b (e.g. gmail)

http://www.screencast.com/t/XoTj285m9

and was expecting to see the cards which are only in group a but not in group b.

But the result are 869 cards which is wired because group a (Daylite) has 442 cards and group b (gmail) has 436 cards.

Could you please help?