It gets worse than just font problems! I've just found one where our rendering makes the Malleus label in Anatomy_of_the_Human_Ear_en.svg head out on a weird angle:
This is only with custom transations, not with unmodified images, so seems likely to be due to our SVG manipulating and not with rsvg.
Actually, sorry, this is probably a completely separate bug! :) But I'll investigate further before opening another ticket.