EPPLus <All versions> - Copy worksheet that contains chart throws Type is a duplicate attribute error

I am trying to copy a worksheet from one workbook to another. For normal worksheets, my code

excelPackage.Workbook.Worksheets.Add("Target", origWS);

works fine. But when the same code is used for a worksheet that contains charts, I get an error

 ''type'' is a duplicate attribute Line 9, Col 150

This seems to be an issue in the XML structure of the excel file

Any help would be much appreciated.