    after using a font for some time, if I unset Wimp$Font,
    various things don't seem to work properly - eg. typing into a
    writable icon leads to the caret disappearing?
      not sure if this is repeatable, but it definitely happened.
    thereafter the system is unreliable, and can often crash, saying
      that the window with the caret cannot be found.

    random background colour at times - sometimes white, green, black...
      if an icon says 'don't fill background' you should use the
      window background colour.

    some menu entries just missing - white foreground colour?

    'Illegal character in font string' sometimes - e.g. when opening
    windows. Can vary for identical actions, so reading garbage values
    somewhere.
    (due to badly terminated strings)

    In some text+sprite icons, the sprite is missing - blanking the
    background on font_paint?
    Perhaps related, *sometimes* on a text+sprite the text background
    partially obscures the icon itself - most noticable on SCSIFiler icons,
      but not always there.

    default action button built using "R6 14" in validation string:
    goes black when pressed, instead of orange.

    Caret sometimes in the wrong position in writable icons, particularly
      when they are initially created.

    The l40 icon type does not work with this font.
