The attached spreadsheet (missing-export-of-protected-cells.ods) contains protected cells. All the cells where you see "#REF!" are protected and therefore cannot be changed unless the user unprotects the sheet. 
However, there is a problem with the export of this file:

This sheet exports nicely to .xls including the protected cells (attachment missing-export-of-protected-cells.xls).
However, it does not export nicely to .xlsx. The cell protection is lost and the user can edit the cells (which should not be the case). (attachment missing-export-of-protected-cells.xlsx )

I assume that protected cells are not handled properly in the XLSX-Export. Please add support for protected cells in .xlsx-files.

Files tested in MS Office 2010