Code analysis of the out-of-the-box Kerberos Node reveals that there is a missing 'return' statement in the happy flow of the node:
release/7.1.0, line 232
Therefore a successful login still results in a FAILED outcome.
After adding a 'return' on line 232 and rebuilding the auth-nodes, the happy flow works as expected:
Please incorporate this in the upcoming release(s).