Setting individual column width sizes for multi column listbox with VB2011 Mac not working

Im working with Excel 2011 on a Mac.
Im trying to use the following VB code to set the column width size for a multi column List Box:

        .ColumnWidths = "20,40,40,100,40,40,40,40"

However each column is appearing to be exactly the same size. Is this some sort of bug with Excel, or is the code different?