Why do Unicode Characters in the PDF Outline show up as, for example, [u1FOA1]?

[T. Kurt Bond]

Why do Unicode Characters in the PDF Outline show up as, for example,
 [u1FOA1]?

Here's an example ms source file:

.\" ===== outline.ms ===========================================
.\" pdf outline fold level
.nr PDFOUTLINE.FOLDLEVEL 3
.\" start out in outline view
.pdfview /PageMode /UseOutlines
.special S Symbola
.SH 1
🂡 Section One
.pdfhref O 1 "🂡 Section One"
.pdfhref M "section-one"
.LP
This is a paragraph.
.SH 1
♂ Section Two
.pdfhref O 1 "♂ Section Two"
.pdfhref M "section-two"
.LP
This is a paragraph.
.SH 1
♀ Section Three
.pdfhref O 1 "♀ Section Three"
.pdfhref M "section-three"
.LP
This is a paragraph.
.SH 1
— Section Four
.pdfhref O 1 "— Section Four"
.pdfhref M "section-three"
.LP
This is a paragraph.
.pdfsync
.\" Local Variables:
.\" compile-command: "pdfroff -ms -mpdfmark -mspdf -e -t -k -KUTF-8
--pdf-output=outline.pdf outline.ms"
.\" End:
.\" ============================================================


It has various Unicode  characters in it in section headers.  (I have
installed the Symbola font for groff to use and specify it as a fallback.
If you are interested, you can get the Symbola font from
https://dn-works.com/ufas/ )

Anyway, in the output file (attached to this e-mail)  the unicode
characters show up fine in the body text fine, but in the PDF Outline the
characters show up as [uXXXX] text instead of the actual character. Does
anybody know why this is?  I know that if I do something similar for
Heirloom troff the PDF Outline *does* contain the Unicode characters.
-- 
T. Kurt Bond, tkurtbond@gmail.com, https://tkurtbond.github.io