Invalid geometry resulting from touching building parts?

[Ylannl]

bag id 0518100000268185

[Ylannl]

Another example:

bag id 0599100010056423, tile 3344

This turns out to be an edge case of a building with a non-manifold edge which splits the building into two parts, but the ground surface is not split correctly and added as a whole to only one of the building parts. The other part does not have a groundsurface.