Don't know if this has anything to do with it, but I remember closing in '05 and for that year I was paying tax on the undeveloped land. It went to the normal tax in '06. Perhaps this applies to you?
I too don't get the disparity between neighbors on my street either. I understand the exemption, and can see some have it and some don't. But some people seem to be taxed much lower still.
Good luck figuring it out.