Buttons disappear when projected
 

When projecting an Excel workbook onto a screen using an InFocus projector,
any buttons that I've placed onto my worksheet (programmed buttons from the
control toolbox - not toolbar buttons) are removed. Only buttons that are
projected are removed (buttons on worksheets within the workbook that are not
projected are not removed) and if I save the workbook and open it again
without projecting those buttons continue to be gone (they don't come back
when I open then the workbook without projecting)

Has anyone ever seen anything like this? Am I missing something really
basic? I'm stumped and therefore, I'm putting out to all of you.