To reproduce:

1. Full protect ("Block all non-admin users") a talk page (e.g something in http://en.wikipedia.beta.wmflabs.org/wiki/Flow_test_talk: namespace) that doesn't exist.
2. Log out.
3. Create the board as an anon.

Step #3 should not be possible.

Regular edit-protection works (except for the error formatting being broken, which is T121137: [betalabs] Blocked user creating a new topic gets malformed error message).