Running the following code will not protect my worksheet. Am I doing something wrong or is this a bug?

Dim ms As New MemoryStream()
Dim wb as new Workbook()

wb.SetCurrentFormat(WorkbookFormat.Excel2007)
wb.Worksheets.Add("TEST WORKSHEET")
wb.Worksheets.Last.Protected = True
populateWorksheet(wb.Worksheets.Last)
wb.Save(ms)

Response.Clear()
Response.AddHeader("Content-Type", "application/vnd.ms-excel")
Response.AddHeader("content-disposition", "attachment; filename=test.xlsx")
Response.BinaryWrite(rpt.ExcelSpreadSheet().ToArray())
Response.End()