Unfortunately there are still problems.
By doing a thorough examination of the database I discovered duplicate entries.
For example the AH2 relation (229600) is 237 times in the database.
Very likely this is also related to only serving a small extract of the world.
I’m trying to reproduce the problem with a test database, probably another problem with osm2pgsql.
The last one is in trac, but still without solution:
https://trac.openstreetmap.org/ticket/4625
Only ways and relations are affected. If you encounter strange renderings of ways or relations, please also report the OSM ID so I can check the database.
I guess this problem existed for a longer time as there had been strange effects before.