Symptoms
Survey URLs are being generated to be opened outside of the Service Portal, even with system property "sn_portal_surveys.sp_survey.email_redirection" set to "true".
Release
Kingston Patch 5
Cause
In the "portals" module, our user did not set any portal to be their default portal.
Resolution
To verify the above, go to the portals module and using the personalization cog (gear), add the "default" column to the list view.
From there, each portal will have either a "true" or "false" value under the "default" column.
In this case, our customer had all portals set to "false". Once they selected the portal they were using and set the default value to "true", the issue was resolved.