I bagged an auction to see the delivery frog, and was duly supplied with my goods and entertained by the little green stoner. Just after he did a yoga pose, as he was setting off I jumped and talked to him - and he stuck around, following me around the street with just an option to "talk to" where he responds with the "Got to be getting off to my yoga class" speech. Wouldn't go away.
He vanished when I changed street, but then I got another visitation where he arrived, may have dropped off (I don't know whether I got anything here since the dropoff would have been a cherry or ten), and posed and zipped off succesfully.
I've raised a couple of bugs against this - once while on the first street to describe the sticky, once on the second to say he'd left. I haven't logged another to describe his second appearance. Is there a better way to continue a bug report than that?