legend problem in mixed line-scatter graph Excel 2007
 

I have a mixed line-scatter chart with 4 line series (labeld 'A' to 'D') and
4 scatter series (labeled 'A mean' to 'D mean') which represent mean values
of respective line series. A to C and respective mean series are linked to
1st Y-axis, D and D mean to 2nd Y-axis. I only want to show legend keys for
line series (A to D). When I delete the non-wanted keys (all mean labels)
Excel shows the correct legend. When I save and reopen file, legend is
messed-up; only serie keys A to C are shown, not D, instead one of the mean
keys is shown. Why is that ?