If this shows on the main page of cPanel, even when your client logs in, then the client's password is the same as the reseller owner's password. Please change your reseller WHM password to a unique password.
If this message only appears when the reseller logs in from WHM (using the cP icon in the List Accounts tool), then this message is normal.
If the message only appears in phpMyAdmin and Fantastico De Luxe, then this is also normal. The reseller owner is not allowed access to those specific cPanel tools. Solution: If you are the reseller and want access to those tools, you will need to login to the client's cPanel directly with the actual cPanel username and password.