Why do requester replies reopen a CLOSED request?

Why do requester replies reopen a CLOSED request?

We are very fond of the fact that a requester's response to a RESOLVED request puts the request back in an OPEN status.  However, our Help Desk team is of the opinion that once the request has been CLOSED (either by the requester or by the system due to lack of response from the requester), there should be no reopening the request.  Any future communications should result in a new request.

Is this a bug or is this by design?

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