Melyik példára gondolsz?
building:levels=3;2 volt a helytelen érték.

https://wiki.openstreetmap.org/wiki/Key:building:part
Where a building has been split into parts, a building outline has still to be drawn of the whole building way and should have the tags building:levels=* and height=*. These values should be the **maximum** of all the building parts.