I think Pivottableextensions are getting confused with
calculated sets created in new Excel 2010 UI.
Sets are listed in Calcs Dropdown. It's then possible to add the set to
pivot table wich leads in Pivotableextensions deleting the set and adding
the mdx Expression as calculated member. I think, if you decide not to support
sets in PT-Extensions it would make sense to check this on filling the combo e.g:
For Each calc As Excel.CalculatedMember In pvt.CalculatedMembers
If calc.Type = Excel.XlCalculatedMemberType.xlCalculatedMember Then