Anything here would just tell you what you have already discovered, that interactive container fields in portals are not supported in Filemaker 12. You can request a change in future releases via the Feature Suggestion Form
or you can post feedback to the feedback section of this forum.
If you would like to describe what you want to do with your portal of interactive container fields, maybe some one can suggest a work around that allows you to get something working for you inspite of this limitation. (There may be ways a list view layout based on the portal table can substitute for your portal.)