Hi, there seems to be bugs in processing OSM simple 3d buildings schema, which I reported at twitter ago. Looks like more complex composed structures with building parts is handled significantly different than other 3D OSM renderer do.
Here is an example from my city of rostock harbour site
(see the the corrupted buildings close to the water and church roofs).
It would be great to fix this issue, before mappers start to see this representation as reference and start modifying the OSM data, which might result in corrupted representation on the other renderers.