Quattro Pro Chart Data Range

I have an X6 file with about 50 sheets.  Each has a chart (bar or line) of data on that sheet.  If I insert a blank sheet before the first one, the Source Data for the charts change, using a data range from the sheet to the left.  So if I begin with:

Sheet 1A Sheet 1B Sheet 2A Sheet 2B Sheet 3A Sheet 3B

and insert a new sheet before Sheet 1A, then the chart on Sheet 3B uses the Source Data range from Sheet 3A.  This occurs for most, but not all of the sheets.  Is there a setting somewhere I've missed?