Subscription Persists After Application Ends

I have a question about how Query Notification works and the objects and data created when a new subscription is created.

Here is what we are doing:

- When the application starts, we call the SqlDependency start method:

SqlDependency.Start( <connection string> )

- For each query we want to monitor, we run the following:

SqlConnection oConnection = new SqlConnection( <connection string> );
oConnection.Open();
SqlCommand oCommand = new SqlCommand( <sql statement> , oConnection);
SqlDependency oDependency = new SqlDependency(oCommand);
oDependency.OnChange += new OnChangeEventHandler( <handler delegate> );
SqlDataReader objReader = oCommand.ExecuteReader();
objReader.Close();

- When the application shuts down, we call the SqlDependency stop method:

SqlDependency.Stop( <connection string> )


We have observed that when we create a new subscription, the following things happen:
1. A row is added to sys.DM_QN_Subscriptions.
2. query_notification_% internal table is created.
3. SQLQueryNotificationStoredProcedure% stored procedure is created.
4. SQLQueryNotificationService% Service Queue is created.
5. queue_messages% internal table is created.

When the application ends, the stored procedure, service queue and queue messages internal table are dropped. The row in sys.DM_QN_Subscriptions and the query_notification_% persist.

When the application is restarted, a new row is added to sys.DM_QN_Subscriptions, but the existing query_notification_% internal table is used.

Is this normal behavior? Or, is there something we should be doing to clean up?

What I am wondering is if there is a threshold where these persistent items become a problem with locking, performance, other?