Ligatures in arabic fonts

Hello guys,
I have bug reported at gentoo [1] which I am not entirely sure how to sort out.

I suspected graphite2 to be the culprit but it is indeed broken with
both system and internal one.
Also if I build the libreoffice on the same machine with generic
./autogen.sh build which pulls most of the packages as internal the
feature works as desired.

So my question is, do you know what area of LO is responsible for this
ligatures and any suggestions how to debug this?

There is testcase attached to the bug which I can reproduce so anyone
who can do so on different distro that built with system libs (debian)
and confirm they have the issue or tell me that the issue is not
present there would be helpful.

Cheers

Tom

[1] https://bugs.gentoo.org/show_bug.cgi?id=405143