Pivot Charts

hi, i'm using a pivot chart to show some data in which the X Axis is a Month,
the Y Axis from 0 to 100, and then 5 series with monthly figures between
0-100 to plot as a line graph.
I've achieved what i'm looking for bar one thing, which is in the 'Data'
section where currently all series are 'ticked' to show on the graph, if I
untick one rather than it remaining in the selction unticked and thus
disapearing off the graph, it disapears altogether from the Data box - also,
the formats are tending to reset themselves as well. Any ideas?