I think I have discovered the issue

I performed the same test on my 9100 laptop and surprisingly, the note is invisible there too, but... connect the 2405 on the 9100's DVI connector,  and extend the desktop and drag the window across on to the 2405 screen and it appears! ... so it must be that analog connected displays (which the 9100 internal must be) cannot render this properly.... and I previously had the 2405 connected to an analog VGA port