Should the seller pay for revised tax prorations based on a new assessment after closing?

Hi Diane,
we sold our home on July 28th, 2011, and i just recieved a letter (Feb 7, 2012) from the buyers of our home that i owe them a check for 231.00 for the price difference in the amount that thier property taxes have now gone up due to the home has gone up in assesed/appraised value. At closing, we paid for property taxes from 1/1/2011-7/28/2011 per the HUD based on the previous years