Ran into this again today.
<asp:BoundField
DataField="FollowUpDate"
DataFormatString="{0:MMM-dd-yy}"
HtmlEncode="false"
HeaderText="Follow Up Date" />
If you are doing a boundfield in an asp.net gridview, and you play on using the DataFormatString, you have to set HtmlEncode to false.
Kinda stupid, but that’s life.