You need to specify the _noAutoClip attribute when you create the window: for example:
WINDOW #1,"COMMAND '.' TO EXIT",,_doc _noAutoClip
FB normally excludes buttons, edit fields and picture fields from the window's "clipping region." When something's excluded from the clipping region, it means that drawing commands can't draw on top of it. By specifying _noAutoClip, you _include_ those objects in the clipping region, so that drawing commands can draw over them.