reset password form shows error on invalid username

Problem/Motivation

When Drupal logins are allowed for some users, the Reset Password form displays an error when an invalid username / email is entered:

Could not load user to do a validation check.

This goes against the standard behavior of this form, which does not confirm or deny the validity of your entry. This will let people probe the site for valid usernames / email addresses.

Proposed resolution

Either disable the display of this error to the user, or make it part of the "Show detailed errors to the user" set of debugging errors.