Shaping text with feature "init" with the font "Prida01" doesn't seem to work correctly

[LaurenzV]

(Originally reported at typst/typst#3924, which uses rustybuzz and not harfbuzz, but I discovered that the same issue seems to exist with harfbuzz)

On this site you can find the font: https://www.glukfonts.pl/font.php?font=Prida01

There are two versions offered, a TTF one and an OTF one.

First I tried shaping with the TTF version, which seems to work fine:
hb-view Prida01.ttf --features init "Hello World" -o out.png

While it doesn't work with the OTF version:
hb-view Prida01.otf --features init "Hello World" -o out.png

At first I thought that this is probably a font issue. But now comes the weird part: I tried subsetting the OTF font with the following command:
hb-subset Prida01.otf -o Prida01.otf "Hello World"

And now the following happens!
hb-view Prida01.otf --features init "Hello World" -o out.png

So I'm not sure what's going on, perhaps it's still a font issue, but it seems weird that somehow subsetting it magically resolves the problem?

(I'm running version 8.4 by the way)

[khaledhosny]

The Prida01.otf file has a morx table while the Prida01.ttf does not, so the shaping is different. The font seems to have been generated by FontForge, so the morx table is probably automatically generated from the GSUB table at build time, most likely by mistake, and it is probably dysfunctional. This is basically a font bug.

[khaledhosny]

hb-subset drops the morx table (it does not support subsetting it), that is why the subset font works as well.

[LaurenzV]

Interesting, thanks for looking into it!