If an e-mail address is being changed in the UCP, but it is not entered again in the "Confirm e-mail address:", the return is: "The e-mail addresses you entered do not match." If left blank, I believe it should say something like: "You must enter your e-mail address again in the confirm e-mail address.", specifically the "Confirm e-mail address:", in order to inform the user they must enter it twice for the forums to consider changing it.
When filling out a "New password:", but the "Confirm password:" is left blank, the return is: "The passwords you entered do not match." and "The current password you entered is incorrect.". Obviously a blank password in the confirm password box will always return a "do not match" and "incorrect" message, and should always be rejected. This should be clarified with a reply back saying something like: "You must enter your password again in the confirm password.". A specific message such as that would be more user-friendly.
Entering some random password in the "Confirm password:", and leaving everything else blank will return "Your profile has been updated.". The reply back should say "No changes were made.", since the original password remains unchanged.
Simply entering a new password in the "Current password:" box only, and clicking Submit, returns the message "Your profile has been updated.". The reply back should be "No changes were made.".
Let's say you click your "Edit account settings" and immediately enter some random e-mail address in the "Confirm e-mail address:" box, but leave your original e-mail address unchanged, then click Submit. The reply back is "Your profile has been updated.". No changes were actually made. The reply back should be "No changes were made."