On 2017-05-02 13:57, Eli Zaretskii wrote:
> Does the problem affect other characters as well, or just these two?

It seems to affect any pair of characters (I tried using (set-fontset-font t '(?← . ?←) (font-spec :name "Symbola") nil) and this prop line:

  -*- prettify-symbols-alist: (("R_PO" . (?A (Br . cl) ?←))); -*-

Clément.