I'm having the same problem, actually. Except that I can't even get them an item before they arrive, even if it's on the counter already and it's what they requested.
Hmm, when I put it on the counter and it's what they want they'll still leave quickly but quickly pop back in, get it, and pay.
Odd. Well, That was happening for me in 0.0.60. I haven't gotten that far yet in the new update, so I guess I'll see if it's still the same once I get there.