sheet-copy turns INDEX to #N/A

[dlh]

When I copy a sheet of my workbook, all the User Defined Functions get replaced with "=#N/A" on the copied sheet.

There are easy workarounds and I don't expect to be duplicating worksheets very often, but I'd really like to understand why this is happening. A full recalculation seems to be triggered at the same time, so that's probably related.

I tried recreating the problem with a really simple UDF in an empty workbook and the problem doesn't occur. So it's caused by something in my project workbook. What should I be looking for?