quesion about glyph ids warning

hi
I'm working on a commercial typeface which has 2 masters(Light and Black) and i use fontmake(sources are in ufo format from fontforge) to generate instances between them with:
`fontmake --interpolate-binary-layout -o ttf -m Pinar_without_kashida.designspace -i`
i receive some repeated warnings(=14 times in every instances) about the glyph ids:
`WARNING:fontTools.ttLib.tables.otTables:GSUB/GPOS Coverage is not sorted by glyph ids.`
also this warning repeated in the same number here in `ttx` log:
```
Dumping "PinarLight.ttf" to "PinarLight.ttx"...
Dumping 'GlyphOrder' table...
Dumping 'head' table...
Dumping 'hhea' table...
Dumping 'maxp' table...
Dumping 'OS/2' table...
Dumping 'hmtx' table...
Dumping 'cmap' table...
Dumping 'loca' table...
Dumping 'glyf' table...
Dumping 'name' table...
Dumping 'post' table...
Dumping 'GDEF' table...
Dumping 'GPOS' table...
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
WARNING: GSUB/GPOS Coverage is not sorted by glyph ids.
Dumping 'GSUB' table...
```
masters are fully compatible, when i generate ttf from the source master and use `ttx` there is no warning, so i can't figure out what's wrong, unfortunately i can't share the project source files but i hope you can give me some clues.