Lars Ingebrigtsen <larsi@gnus.org> writes:

> Is it possible that Gnome Shell (or something) is somehow interfering
> here and substituting other icons?

D'oh!

All this is just user error on my part.  I had changed the font scaling
in gnome-tweaks to x2.7, and not done any proper scaling.

Now, with a 200% scaling (and a x1.3 font scaling), I get: