HI Lene
Thanks for having a look.  yes I've set the button .style
=MsoButtonIconAndCaption when i created the control, and can see the image
originally assigned to the control.
Problem is I can't change the displayed image unless I can actually see it
(I don't mean .visible). I.e it has to be displayed on a commandbar to
change. It won't change if on a popup on the same bar, nor a menu bar popup
etc.

At the risk of being very boring, here's some code that shows the problem.
it can change the  "Button1" image, but not for "Button2":

Sub aChangeFace() 'change the faceID shown
   x = "Button1"
   If MsgBox("button 1 (y) or 2(n)", vbYesNo, "change faceID") = vbNo Then
x = "Button2"
   With Application.CommandBars.FindControl(Tag:=x)
        waz = .FaceId
       If .FaceId = 1088 Then
           .FaceId = 1087
       Else
           .FaceId = 1088
       End If
       MsgBox "now= " & .FaceId, , .Caption & " faceID was " & waz
   End With
End Sub
Sub aMakeMyBar()
   Dim myMenu As CommandBar
   Dim btn As CommandBarButton
   Dim subMenu As CommandBarPopup

   On Error Resume Next
   Application.CommandBars("MyBar").Delete
   On Error GoTo 0

   Set myMenu = Application.CommandBars.Add("MyBar", msoBarTop, , True)
   myMenu.Visible = True
   With myMenu.Controls
      Set btn = .Add(Type:=msoControlButton)
      With btn
         .Style = msoButtonIconAndCaption
         .FaceId = 123
         .Caption = "Button1"
         .Tag = "Button1"
         .OnAction = "ButtonAction1"
      End With
     
      Set subMenu = .Add(Type:=msoControlPopup)
      With subMenu
         .Caption = "subMenu"
         .Tag = "subMenu"
         Set btn = .Controls.Add(Type:=msoControlButton)
         With btn
            .Style = msoButtonIconAndCaption
            .FaceId = 123
            .Caption = "Button2"
            .Tag = "Button2"
            .OnAction = "ButtonAction2"
         End With
      End With
   End With
End Sub
Sub ButtonAction1()
  MsgBox "Button 1 Click."
End Sub
Sub ButtonAction2()
  MsgBox "Button 2 Click."
End Sub