Or here’s another example. Which shows right and wrong use of duplicated fields and (horror or horrors) disables cut&paste.
The only requirement for a confirmation field is when entering a value that is not visible, i.e. a password. For anything else I can see the value I’ve typed and “confirm” it’s correct without retyping. Don’t make me repeat myself.
If worried about validity, beef up your error-checking. Don’t delay me with pointless re-typing (or more usually, cut&pasting).
And another thing. While making me repeat myself is bad enough, making me repeat myself and then disabling cut&paste in the repeated field gets you your own special corner of hell.