Nocturne's Ultimate Dash vs Knockdown effects

Is there a reason why the stun will apply when he is done with the dash?

During the dash, Nocturne cannot be disabled. Yet he ends up disabled if he flies through Veigar's cage at the end of the dash.

Olaf's immunity to disables doesn't get him stunned when he runs through Veigar's cage, nor does it apply afterward.

Please fix this inconsistency.