It looks as if the mongos can create databases with invalid names, leading to subsequent problems draining the shard with the invalid db name (see https://groups.google.com/group/mongodb-user/browse_thread/thread/7186e51d5a31bcd2?pli=1).

Here's a reproduction case for creating an entry in config.databases with an invalid name:

mongos> config=db.getSiblingDB("config")
config
mongos> config.databases.find()

{ "_id" : "admin", "partitioned" : false, "primary" : "config" } { "_id" : "test", "partitioned" : false, "primary" : "repl0" }

mongos> foo=db.getSiblingDB("foo ");
foo
mongos> foo.c.insert(

{ _id : 1 }

);
invalid db name: foo .c
mongos> config.databases.find()

{ "_id" : "admin", "partitioned" : false, "primary" : "config" } { "_id" : "test", "partitioned" : false, "primary" : "repl0" } { "_id" : "foo ", "partitioned" : false, "primary" : "repl1" }

mongos> db.adminCommand(

{ listDatabases : 1 }

);
{
"databases" : [
{
"name" : "test",
"sizeOnDisk" : 218103808,
"empty" : false,
"shards" :

{ "repl0" : 218103808 }

},

{ "name" : "config", "empty" : false, "sizeOnDisk" : 201326592 }

],
"totalSize" : 218103808,
"totalSizeMb" : 208,
"ok" : 1
}