question about NotoSansMono: Is this a source or a fontmake issue?

source: https://github.com/googlei18n/noto-source/blob/master/src/NotoSansMono-MM.glyphs

Is this a source or a fontmake issue? If source what should I advise the provider?

============= NotoSansMono-MM.glyphs ==============
INFO:fontmake.font_project:Building master UFOs and designspace from Glyphs source
INFO:glyphsLib:Parsing .glyphs file
INFO:glyphsLib:Casting parsed values
INFO:glyphsLib:Loading to UFOs
INFO:glyphsLib.util:Writing master_ufo/NotoSansMono-Light.ufo
INFO:glyphsLib.util:Writing master_ufo/NotoSansMono-Regular.ufo
INFO:glyphsLib.util:Writing master_ufo/NotoSansMono-SemiBold.ufo
INFO:glyphsLib.util:Writing master_ufo/NotoSansMono-Bold.ufo
INFO:glyphsLib.util:Writing master_ufo/NotoSansMono-CondensedLight.ufo
INFO:glyphsLib.util:Writing master_ufo/NotoSansMono-Condensed.ufo
INFO:glyphsLib.util:Writing master_ufo/NotoSansMono-CondensedSemiBold.ufo
INFO:glyphsLib.util:Writing master_ufo/NotoSansMono-CondensedBold.ufo
INFO:fontmake.font_project:Building interpolation-compatible TTFs
INFO:fontmake.font_project:Converting curves compatibly
INFO:cu2qu.ufo:New spline lengths:
1: 530
2: 6659
3: 467
4: 52

INFO:fontmake.font_project:Saving TTF for NotoSansMono-CondensedLight
INFO:fontmake.font_project:Saving TTF for NotoSansMono-Bold
INFO:fontmake.font_project:Saving TTF for NotoSansMono-Condensed
INFO:fontmake.font_project:Saving TTF for NotoSansMono-Light
INFO:fontmake.font_project:Saving TTF for NotoSansMono-SemiBold
INFO:fontmake.font_project:Saving TTF for NotoSansMono-CondensedBold
INFO:fontmake.font_project:Saving TTF for NotoSansMono-Regular
INFO:fontmake.font_project:Saving TTF for NotoSansMono-CondensedSemiBold
INFO:fontmake.font_project:Building variable font variable_ttf/NotoSansMono-VF.ttf
INFO:fontTools.varLib:Internal master locations:
[{'weight': 26.0, 'width': 100.0},
{'weight': 90.0, 'width': 100.0},
{'weight': 151.0, 'width': 100.0},
{'weight': 190.0, 'width': 100.0},
{'weight': 26.0, 'width': 70.0},
{'weight': 90.0, 'width': 70.0},
{'weight': 151.0, 'width': 70.0},
{'weight': 190.0, 'width': 70.0}]
INFO:fontTools.varLib:Internal axis supports:
{'weight': [26.0, 90.0, 190.0], 'width': [70.0, 100.0, 100.0]}
INFO:fontTools.varLib:Normalized master locations:
[{'weight': -1.0, 'width': 0.0},
{'weight': 0.0, 'width': 0.0},
{'weight': 0.61, 'width': 0.0},
{'weight': 1.0, 'width': 0.0},
{'weight': -1.0, 'width': -1.0},
{'weight': 0.0, 'width': -1.0},
{'weight': 0.61, 'width': -1.0},
{'weight': 1.0, 'width': -1.0}]
INFO:fontTools.varLib:Index of base master: 1
INFO:fontTools.varLib:Building variable font
INFO:fontTools.varLib:Loading master fonts
INFO:fontTools.varLib:Generating fvar / avar
INFO:fontTools.varLib:Building variations tables
INFO:fontTools.varLib:Generating MVAR
INFO:fontTools.varLib: xhgt: OS/2.sxHeight [528, 536, 546, 553, 528, 536, 546, 553]
INFO:fontTools.varLib: stro: OS/2.yStrikeoutPosition [317, 322, 328, 332, 317, 322, 328, 332]
INFO:fontTools.varLib:Generating gvar
INFO:fontTools.varLib:Generating HVAR
INFO:fontTools.varLib:Merging OpenType Layout tables
Traceback (most recent call last):
File "/usr/local/bin/fontmake", line 9, in
load_entry_point('fontmake==1.2.4.dev0', 'console_scripts', 'fontmake')()
File "/usr/local/google/home/marekj/newrel/fontmake/Lib/fontmake/__main__.py", line 182, in main
project.run_from_glyphs(glyphs_path, **args)
File "/usr/local/google/home/marekj/newrel/fontmake/Lib/fontmake/font_project.py", line 379, in run_from_glyphs
designspace_path, instance_data=instance_data, **kwargs)
File "/usr/local/google/home/marekj/newrel/fontmake/Lib/fontmake/font_project.py", line 435, in run_from_designspace
interpolate_layout_from=interpolate_layout_from, **kwargs)
File "/usr/local/google/home/marekj/newrel/fontmake/Lib/fontmake/font_project.py", line 495, in run_from_ufos
self.build_variable_font(designspace_path)
File "/usr/local/google/home/marekj/newrel/fontmake/Lib/fontmake/font_project.py", line 228, in build_variable_font
font, _, _ = varLib.build(designspace_path, finder)
File "/usr/local/google/home/marekj/newrel/fonttools/Lib/fontTools/varLib/__init__.py", line 576, in build
_merge_OTL(vf, model, master_fonts, axisTags, base_idx)
File "/usr/local/google/home/marekj/newrel/fonttools/Lib/fontTools/varLib/__init__.py", line 384, in _merge_OTL
merger.mergeTables(font, master_fonts, axisTags, base_idx, ['GPOS'])
File "/usr/local/google/home/marekj/newrel/fonttools/Lib/fontTools/varLib/merger.py", line 106, in mergeTables
self.mergeThings(font[tag], [m[tag] for m in master_ttfs])
File "/usr/local/google/home/marekj/newrel/fonttools/Lib/fontTools/varLib/merger.py", line 93, in mergeThings
self.mergeObjects(out, lst)
File "/usr/local/google/home/marekj/newrel/fonttools/Lib/fontTools/varLib/merger.py", line 70, in mergeObjects
mergerFunc(self, value, values)
File "/usr/local/google/home/marekj/newrel/fonttools/Lib/fontTools/varLib/merger.py", line 93, in mergeThings
self.mergeObjects(out, lst)
File "/usr/local/google/home/marekj/newrel/fonttools/Lib/fontTools/varLib/merger.py", line 70, in mergeObjects
mergerFunc(self, value, values)
File "/usr/local/google/home/marekj/newrel/fonttools/Lib/fontTools/varLib/merger.py", line 93, in mergeThings
self.mergeObjects(out, lst)
File "/usr/local/google/home/marekj/newrel/fonttools/Lib/fontTools/varLib/merger.py", line 70, in mergeObjects
mergerFunc(self, value, values)
File "/usr/local/google/home/marekj/newrel/fonttools/Lib/fontTools/varLib/merger.py", line 97, in mergeThings
assert all(out == v for v in lst), (out, lst)
AssertionError: ((2, [3, 2, 2, 2, 3, 2, 2, 2]), 'int', '.FeatureCount', 'FeatureList', '.FeatureList', 'GPOS', '.table', 'table_G_P_O_S_')