Selecting the Shavian section, I expect to see the appropriate glyphs displayed.
Instead, all of the boxes are blank. On right clicking a box, the popup appears
with no glyph, but specifying that the font used is Andagii (a truetype font).
Andagii is not the font I have selected, but it does contain the appropriate
glyphs at the correct positions, as gfontview attests (Mozilla also displays the
glyphs, though I cannot tell for sure that it is using the same font).

It seems then that gucharmap knows that Andagii has the correct glyphs, but is
simply failing to display them.