Is this one of the working browser forms that you are viewing in the client, or did you make a new form that is for rich client only, and it is not working?
It definitely works in both. I would guess that if this is a new form, then you probably just got the syntax wrong on the Contact Selector nodes. They can be very finicky.
As a test, you can go to an existing browser-based form in one of your other libraries and open it in InfoPath (down arrow, edit in Infopath) to ensure the Contact Selectors work for you in the client.