Closed Unassigned: Can't set header on non empty header [9500]

I am using this code to set the header on a document that already contains headers(first page and odd even) and it does not work.

pageSetup.Header.Center.AddText("first", XLHFOccurrence.FirstPage);
pageSetup.Header.Center.AddText("odd", XLHFOccurrence.OddPages);
pageSetup.Header.Center.AddText("even", XLHFOccurrence.EvenPages);

if i delete the headers, it does work.

using pageSetup.Header.Center.Clear(); does not work either.
Comments: Can't replicate.