Excel 2007 Charts, Format data point.
 

I have several column charts displayed on a tab sheet (worksheet) of an Excel
2007 workbook. Some charts have a single series of data, others have more
than one series per category. I want to visually differentiate some of the
columns/bars in a series as representing older (vs. current) data. I can do
this by double clicking on each affected bar to [Format data point] (as
opposed to [Format data series]). From here, I can change the attributes
(such as fill color or border style) of a single bar. (Cool.) On the charts
with more than one series this works fine. However, on charts with only one
series, any change to a single bar via [Format data point] will inexplicably
replace the single series legend entry with the entire list of X axis
category labels. How can I fix this?