To protect a reference to sheet1, say, before copying sheet containing reference to sheet1, prefix sheet1 with $ sign. Then reference to sheet1 becomes $sheet1 in original sheet and remains $sheet1 in generated copy.
I'm not really sure if it should normally be necessary to protect references embedded in sheets to other sheets, but it is at least it's a work around!
To protect a reference to sheet1, say, before copying sheet containing reference to sheet1, prefix sheet1 with $ sign. Then reference to sheet1 becomes $sheet1 in original sheet and remains $sheet1 in generated copy.
I'm not really sure if it should normally be necessary to protect references embedded in sheets to other sheets, but it is at least it's a work around!