Name Of Active Workbook From Add-in

I have an add-in (MyAddin.xla) that is called from my open_workbook event in my workbook (MyBook.xls):


Private Sub workbook_open()

AddIns("MyAddin").Installed = False
AddIns("MyAddin").Installed = True

ThisWorkbook.Activate

Run "MyAddIn.xla!WbookOpen"

End Sub

I put this in my WbookOpen procedure:


Sub WbookOpen(pWorkbook As Workbook)

MsgBox "Wbook Open Active workbook is " & ActiveWorkbook. Name
End Sub

The message displayed is:
Wbook Open Active workbook is MyAddin.xla

I thought this would be:
Wbook Open Active workbook is MyBook.xls.