When running show collections (show tables, db.getCollectionNames()), the result is always empty (on sharded, as well as non-sharded collections). However I can verify the collections existence by getting a cursor on its data (db.collection.find())m which works just fine.

The setup is a sharded testsetup with 3 shards, each having an arbiter, three config servers and a mongos. The problem occurs on the mongos as well as on individual shards.