Under a user the option to Change Login/Copy User has several flaws. For one, it seems there is no actual way to just change login information, you have to destroy a user, create a new one. That flaw then falls prey to the bug, which is "Create new user with same privileges" is no longer true. In the past this worked, but in 4.0.5 the new user has NO privileges to anything, where it's expected and used to be that database specific rights were replicated as expected in the new user. This means these all have to be set after the user is cloned, and in the case of just trying to change a password, you now have to go reset everything for the "new" user that has replaced the old one but has no rights.