Not all unicode characters display correctly

I'm trying to use matchbox-keyboard with a keyboard.xml file that only uses unicode characters in places where a standard keyboard would have text, e.g., ⇱ for HOME. Unfortunately some of the unicode characters I want to use (⎖ ,⎗ and ⎀ ) only appear as the generic box for an unavailable character. The characters are in the font(s) I've tried (I can enter them in a text file with gedit and in a Libre Office Writer file) so I am stymied.