That's the same as a tiny little guy who lived down the street. Haven't been seeing him around so I'm not sure if he's still... around. When my shihtzu walks by, all 2-3 lbs of him would bark, stop, come running up to a foot or two away, runs back up the steps of the house (standing by or behind the owner who's sitting there) and resumes his barking. He was such a cute little guy.
As cute as yours and that little boy is, I'm glad my girl doesn't bark at doorbells nor does she bark when someone knocks. She saves her very healthy vocals for other encounteres.
You should video tape your girl doing that! Would be cute to document and watch! *grin*