Excel 2013 VBA Sheets.Add doesn't return new s

So my code was working fine, until IT upgraded me to Excel 2013 and the SDI interface. Now it looks like the Sheets.Add function doesn't return the proper worksheet. The template is added to the correct workbook (Template1) but when I use the returned worksheet, it's referencing a sheet from the active workbook, before all the VBA code ran.

Public Function Worksheet_AddTemplate(TargetBook As Excel.Workbook, _
                                      TemplateFile as String) As Excel.Worksheet
Dim ws As Excel.Worksheet
    Debug.Print TargetBook.Name     'Output-->Template1
    Set ws = TargetBook.Sheets.Add( _
                After:=TargetBook.Sheets(TargetBook.Sheets.Count), _
                Type:=TemplateFile)
    Debug.Print ws.Parent.Name      'Output-->Book1
    Set Worksheet_AddTemplate = ws
    Set ws = Nothing
End Function

Can someone else verify that this is happening to you with Excel 2013, and that there isn't something that I'm missing here.

Thanks

P.S. I use a similar routine to create the template workbook/first sheet with no issues.

Edit: The Code is being called from an Add-In. Here is how I call the Function, more or less (I've simplified the routines because it would be too long otherwise)

Private Sub ImportDataFile()
Dim wb As Excel.Workbook
Dim ws As Excel.Worksheet
Dim sUnit As String, sTemplateFile As String
Dim u As Integer, nUnits As Integer

    Application.ScreenUpdating = False
    Application.EnableEvents = False
    ' ...Some setup stuff that I wont bother you with
    sTemplateFile = Environ("Temp") & "\Template1.xlt"
    For u = 0 To nUnits - 1     
        If wb Is Nothing Then
            Set wb = Workbook_NewTemplate(sTemplateFile)
            Set ws = wb.Worksheets(1)
        Else
            Set ws = Worksheet_AddTemplate(wb, sTemplateFile)
        End If
        ws.range("H6") = sUnit
        ' More Loops & writing to cells
        For i = 0 To g_Data(f).ItemCount - 1
            ' Blah, blah, blah      
        Next
    Next
    Application.ScreenUpdating = True
    Application.EnableEvents = True
End Sub

I've noticed that if I add 2x DoEvents anywhere in between creating the workbook and adding the second sheet it will work as it did before.

Also, if I use this code in the Worksheet_AddTemplate function it seems to work...

Set wb = Application.Workbooks.Add(Template:=TemplateFile)
Set ws = wb.Worksheets(1)
ws.Copy After:=TargetBook.Sheets(TargetBook.Sheets.Count)
Set ws = TargetBook.Sheets(TargetBook.Sheets.Count)