Clients receiving Issue Notification when Global Preference set to NEVER

We have clients that are receiving issue notifications even when we deliberately set the Setup > Issues > Issue Preference > Send Customer Notifications When  > NEVER.  However we found there is a loophole where clients can override our desire to never send them an email. 

This has already caused some very upset customers who do not understand how we use issue records internally.  We recognized this would be the case, and so we thought we denied them access.  After calling NS support, they notified us that our client's have a "right" to see this information if they adjust their preference in the customer center.  This is horrible design.  We own the NetSuite instance not our customers.  We ought to be able to prohibit them from receive emails.  Clients only have exposure to cases in the client center, not issue.