Preparation: Create a database named "[a-z]+" and create a collection name "test" and shard it.

From the mongo shell (connected to mongos):

1. db.getSiblingDB("[a-z]+").dropDatabase();
2. use config
3. db.databases.find() // [a-z]+ is not listed -> OK
4. db.collections.find() // [a-z]+.test is still there -> BUG