Filter raises 'Polygon begins with an inner ring' without changing that data

I used tippecane with -C 'python myfilter.pyo' and got an error

Polygon begins with an inner ring

So I reduced the filter to just

-C 'cat'

And I get the same error

But removing the -C script completely doesn't raise an error

My full command:

tippecanoe -n "routing tileset" \
  -P -Z11 -z11 -D12 -d13 --no-feature-limit \
  -x OBJNAM -x FID -x water -x natural -x cc -x tile_x -x tile_y -x error \
  -o routing.mbtiles \
  -C 'cat' \
  --clip-bounding-box=-68.500000,44.583290,-66.500000,46.583290 \
  -Losmwt2:<(cat ./dist/osm/geojson/osm.water.geojsonseq;) 

So it seems like the filter raises 'Polygon begins with an inner ring' without changing that data

Reproduce the supplied tippecanoe command with -C 'cat', then without the filter, using the referenced GeoJSON sequence input and clip bounding box. Trace the filter and polygon-validation path to determine why the filter changes the outcome despite not changing feature data; done means the discrepancy is explained and the reported behavior is corrected or documented.