Button on custom toolbar appears only after mouse hovered over it

Hi all,

If have a toolbar that is created when I open a certain workbook; there
are three buttons on the toolbar. The code to add one of the buttons
looks like this:

' Button for email configuration.
With cbcCustomToolbar.Controls.Add(Type:=msoControlButton)
.FaceId = 2569
.TooltipText = "E-mail instellingen wijzigen"
.OnAction = "ShowMailConfig"
.Style = msoButtonIcon
End With

Strangely enough, the first two buttons show up as expected. The third
one (generated with the code above) is not there, but as soon as I
hover with the mouse above the place where it's meant to be, the button
appears and everything is fine. Why isn't it already there when I open
the workbook?

This happens with Excel 2003.