This isn't a Perl question, but I'll address it anyway. :)

In general, HTML forms with the same-named controls will be 'sticky' such that the previous values entered will be populated in a subsequent display of the form.

Usually the way validation errors are handled is to say, "Validation failed for reason X" and re-display the form (often with the label to the offending field bolded), rather than asking the user to press 'Back' (as was noted in Joost's response).