Why does config db not backup from remote server

We have just converted our enterprise servers to community (v6.0.6). All is running well. What is puzzling is: when I perform a backup using mongodump, from a member of the cluster (replica set), the config db is included in the dump. However, if I perform the same backup, using the same config file, from a remote server that is not part of the replica set, the config db is not part of the dump.
Can someone explain why?
I suspect this was also occurring on the enterprise binaries, but I am not certain.

This is the dump statement (sanitized) I am using (the user executing the command is a member of the mongod and mongodb groups in both cases):

$  /usr/bin/mongodump --username=<masteruser> --config="/home/<mongouser>/.MdbConf" --authenticationDatabase=admin --out=/mnt/MongoBak/MongoBakUps/FullDump-$(date +%F.%H%M%S) --readPreference='{mode: "secondary", tagSets: [ { "NickName": "read" } ], maxStalenessSeconds: 120}'

The contents of the .MdbConf file contains only the password and uri:

$  cat ~/.MdbConf
password: <masterpasswd>
uri: mongodb://<masteruser>@mdb00.<domain>:27017,mdb01.<domain>:27017,mdb02.<domain>:27017/?authSource=admin&tls=false&replicaSet=rs0

Thanks in advance for your input

--db=<database>, -d=<database>

Specifies a database to backup. If you do not specify a database, mongodump copies all databases in this instance into the dump files.

Maybe that’s because your remote server doesn’t have a config database?