Why chart's reference is changed when open an excel?

[landfox]

hello OOo,
I have two excel files with charts, I want to merge these sheets in the files into one document. For each file, there are two sheets, one sheet has data, the other sheet has charts based on the first sheet.

Unfortunately, when I try to open an excel file with Openoffice Calc, the chart is empty. When I check it's data range, I found that the rang has been changed to the current sheet that the chart is located, other than its original location in another sheet! Is this a bug in Openoffice 2.1?

I would like to use Openoffice sdk to merge these two files, how can I merge these two excle file without wrong data rang for the charts?

thanks so much,
Davy Lee