I used to be a hiring manager, and if this had happened with an applicant I would have been horrified!!! Just as Alison says, this person is sending a very loud signal that they think it's fine to go charging in like a bull to do things their own way without regard for how it affects others or whether it's consistent with management directions. You do want employees who can take initiative, but for goodness' sake, it has to be balanced with common sense!