Commented Unassigned: copied sheet as a reference to the original sheet for the drawing [15250]

if you copy a sheet and delete the original one, all drawing on the copied sheet will be lost and Excel will ask to repair the sheet. (unreadable content)

step to reproduce

1. create a new excel file with Excel 2007 and stay on sheet1
2. Go to insert
3. Click picture
4. Select a picture
5. Save
6. Close Excel

run this code on it
```
using exfile as new excelpackage(new fileinfo("excel file from step 1")

exfile.workbook.worksheets.copy("sheet1","copiedSheet")

exfile.workbook.worksheets.delete("sheet1")

exfile.save()
end using
```

open the Excel file, you wil have repair it and the image are lost.
Comments: found this issue while changing the sheet, from embed picture to actual picture, to bypass the issue of https://epplus.codeplex.com/workitem/15248