Database constraint triggered in +settopics page.

Steps to reproduce (using sample data):
1. Log in as Sample Person;
2.
http://features.launchpad.dev/distros/kubuntu/+spec/cluster-installation/+linksprint
3. Select 'Ubuntu DevSummit Guacamole' and click 'Add';
4. Log in as sabdfl;
5. http://launchpad.dev/sprints/uds-guacamole/+settopics
6. Select 'cluser-installation' spec and click 'Accept';
7. Crash with an IntegrityError.

2006-08-21T17:52:59 ERROR SiteError
http://launchpad.dev/sprints/uds-guacamole/+settopics
Traceback (most recent call last):
  File
  "/home/matsubara/devel/launchpad/trivial/utilities/../lib/canonical/launchpad/webapp/adapter.py",
  line 325, in execute
      return self._cur.execute(
      IntegrityError: ERROR: new row for relation "sprintspecification"
      violates check constraint "sprintspecification_decision_recorded"