`cloneable` in superclass

I'm getting this message that I don't fully understands:

```
Superclass ecmwfr_service has cloneable=FALSE, but subclass ecmwfr_ds has cloneable=TRUE. A subclass cannot be cloneable when its superclass is not cloneable, so cloning will be disabled for ecmwfr_ds.
```

Just wanted to share it in case you've haven't seen this. 