Form Validation Class - Get validated values?

[eluser]Colin Williams[/eluser]
So, you contend that the bug is

If you define a field to be validated using the form validation library and it isn’t included in the $_POST array, the form validation library will still validate it including running any callback functions, but will not add the processed value back into the $_POST array at the completion of the validation.

I still can't fathom how a "processed" value comes from a value that never existed. But regardless of that, what is the expected behavior? What should the validation class do?