The messages released from the spam quarantine are automatically submitted to Symantec as misidentified spam.
This behavior is due to the Customer-Specific Spam Submissions feature being enabled, along with the "Submit to Symantec Security Response" option being checked under:
Spam > Settings > Quarantine Settings
When this setting is active, any message released from quarantine is automatically submitted to Symantec for further analysis as a potential false positive.
To prevent automatic submissions and switch to manual control:
Go to Spam > Settings > Quarantine Settings
Uncheck "Submit to Symantec Security Response"
With this option disabled, messages will only be submitted to Symantec Security Response when done so manually.