"Arrival" date reverts after choosing "departure" in Windows xp..

"Arrival" date reverts after choosing "departure" in Windows xp..

Hi, we're using the jquery ui date picker for our accommodations search tool... visitors select a arrival date and then a departure date and then click search... everything is working good except for on Windows XP... If I Tuesday on arrival date a couple months out and then select a departure date it will cause my arrival date to revert back to some other date.  Doesn't seem to be happening on any other operating system.
 Has anyone seen this before?  Any potential solutions would be much appreciated.  Thanks very much.
test url here: http://vuong01.dreamhosters.com/