Rendering problems with Khmer text containing U+17D2 and U+17C2

gnome-terminal has some problems displaying Khmer text:

The Khmer Sign Coeng (U+17D2) functions to indicate that the following Khmer letter is to be rendered subscripted.

The Khmer Vowel Sign Ae (U+17C2) needs to be rendered in front of the preceding character.

However, that doesn't work in gnome-terminal.

See attached screenshots how things are supposed to look like (as rendered in gedit) and how they look in gnome-terminal:

ខ្មែរ (U+1781 U+17d2 U+1798 U+17c2 U+179a)

word fragments:
ខ្ម (U+1781 U+17d2 U+1798)
ខែ (U+1781 U+17c2)

System information:

$ lsb_release -rd
Description: Ubuntu 18.04.5 LTS
Release: 18.04
$ apt-cache policy gnome-terminal
gnome-terminal:
  Installed: 3.28.2-1ubuntu1~18.04.1
  Candidate: 3.28.2-1ubuntu1~18.04.1
  Version table:
 *** 3.28.2-1ubuntu1~18.04.1 500
        500 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     3.28.1-1ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu bionic/main amd64 Packages