Job Import Plugin: Fields remain populated till "Done" succeeds

I just tried the Job Import Plugin (1.3.1) after a colleague told me he got errors importing jobs from another Jenkins. To my surprise, I still saw the URL and username pre-populated as he had entered it before. Only when import was successful and "Done" clicked it seems to reset those fields. Until then even across different sessions and browsers you see the previously entered login details (including a yet masked out PASSWORD).