The Mistletoe value chart for the last month is displaying Jan 01, 1970 so the start of timestamp.
For all the other options the graphs are shown correctly.
I assume the problem has something to do with no purchase being made in the last month, but it should probably display something other than the timestamp of 0. Perhaps the date of the last time a purchase was recorded.
Screenshot
[image: i.imgur.com]
Extra note: The item info you page for Mistletoe seems to be broken too. http://www.torn.com/iteminfo.php?ID=305
EDIT: fixed the screenshot not displaying.