I'm a maintainer of the Leaflet Widget module.

While developing the module, I realized, that the geofield is not the right backend to save GeoJSON data.

Geofield always converts and saves geodata in the WKT format. When using the Leaflet Widget module, I had to convert back the WKT data to geojson. But I realized, that a lot if features got lost during the conversion. Especially all layers were merged into a single multipolygon.