Negative Standard Deviation

There is a web site www.barchart.com devoted to stocks and other financial instruments. One of the statistics they support for stocks is Standard Deviation, which is supposed to represent the variability of the difference of the stock's price on a particular day from that on the previous day. Some of the stocks are characterized as having negative standard deviation. I have written the webmaster that a standard deviation must be either zero or positive but have received no response. What is going on there?