FMC incorrectly programmed, A/P did what it was meant to. Crew identified problem, disconnected and completed approach without incident.
Nothing to see here. Mistake get made, errors identified and managed.
Had the crew persisted with Automatics, then it may have become an issue. Had the crew not been competent to manually correct the problem, then it may have become and issue.
At VAI A/P is deemed as the most appropriate method of mitigating the effects of fatigue. In this instance it didn't work.