I noticed this while working with a Processor sample. There are a couple of problems I want to tackle as part of this:

• Using a client that's been closed doesn't return an error in all cases. In particular, calling GetEventHubProperties() can bypass the "open" check for the client.
• When stopping a Processor the individual clients can return an errorString("client has closed") which is actually okay and expected. We should return a new ErrorCode for that so people can ignore it cleanly.