adding asp:placeholder doesn't add required code to designer file

All,
On my site.master im trying to add a placeholder however im having trouble referencing it and it seems for some reason VB isn't adding the required
    Protected WithEvents adminstuff As Global.System.Web.UI.WebControls.PlaceHolder
to the designer window. any ideas why this might happen? When i add it manually it stays there until the designer regenerates itself, at which point it disappears.

is this not possible in a master page???