Excel 2007 : PivotChart Legend Omitting Series

Hello,

I have a pivotchart, and it is not displaying whichever series I have at the top of the "Values" field.

Whichever series is in the first position is not shown on the legend, I can swap them around and then they will show up but whichever one is in the first position (and in one case both first and second) will not show up.

The series still shows on the chart, just not referred to in the legend.

Has anyone ever experienced this problem?