https://www.openstreetmap.org/way/138427577 should also have building:levels=8 because it's the level of the parts (without the min level correctly indicated on way 1226185078)

see : https://wiki.openstreetmap.org/wiki/Key:building:part (Tags to use in combination) 

otherwise it's means there is a 2 levels building parts inside a building with 8 levels (https://wiki.openstreetmap.org/wiki/Key:building:levels section : Buildings with parts that don't start at ground level) 

I know it's a little conter intuitive but it's how data user cosume this and render a mostly empty buidling inside.