I don't quite understand why that could be a problem. If a user is already subscribed to bug mail then definitely subscribing them to the bug directly will not do any harm - they won't be receiving more mail than they would have otherwise.
I don't quite understand why that could be a problem. If a user is already subscribed to bug mail then definitely subscribing them to the bug directly will not do any harm - they won't be receiving more mail than they would have otherwise.