Constructium: Combining characters sometimes glitch?

[ethus3h]

Hello!

I was looking to add some characters to Constructium so I could use it for a project, since it looks like the font is generally what I want, but I ran into the problem that not all diacritics seem to work reliably, even ones that work in Gentium:

Screenshot

The A with the combining breve worked just fine, though, even though it seems like a similar case 🤷‍♀️

This is in LibreOffice 7.4.7.2 on Debian Linux.

When I tried adding my own diacritic in the Private Use Area, it exhibited the same bug as this character (U+033D COMBINING X ABOVE); I tried both with the official Constructium and my patched one.

I'm hoping to implement support for my scripts and other characters and perhaps eventually submit them to the UCSUR, I'm kind of stumped with the diacritics problem though.

Thank you in advance if you get the chance to look into it!

(For the curious...)