kendzi,
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There is link to message here and link to osm-file with examples is broken there.
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About deactivation of volume rendering of building outlines - I want to add, that joining to relation type=building is not the only simple method to recognize building, which has dividing to parts. Another variant is detecting a tag building:parts= . On the one hand, if you don’t want, of course, you can not add this tag, but, on the other hand, you can use this tag right now in that buildings, which already have it (more that 1.000 buildings have this tag at this moment).
Could you, please, deactivate volume rendering of buildings (building= ), which also have tag building:parts= ?