Functions are replaced with the wrong results when coping worksheets

[George]

I wrote a simple function that interpolates data on a worksheet.
My problem occurs with the following steps:
A copy of the original worksheet with the functions is created.
Then the data on the original worksheet is change.
A new copy of the revised original worksheet is created.

Looking at the first copy of the worksheet the functions are recalculated or replaced with the results from the revised original worksheet.

George