There is currently a small inconsistency between how the arabic language category and the glyphs.xml file handles yehFarsi-ar and it’s derived glyphs.
The glyph.xml file name them as follows.
yehFarsi-ar
yehFarsi-ar.fina
yehFarsi-ar.medi
yehFarsi-ar.init
The language category on the other hand names them
yeh-farsi
yeh-farsi.medi
yeh-farsi.init
yeh-farsi.fina
This causes conflict when you try to generate them through the language category’s glyph generator.
The names for the glyphs in the language category should be changed to the ones used in the glyphs.xml file.