this is not a bug, the validation failure is stored in a session, the session will not be cleared until the form submits correctly.
if you look at the code for the validation, you will see a line that sets the session. for example on the update page you sent, it looks like this:
$_SESSION['WAVT_updatemember_Errors'] = "";
the session name will change based on the page name.
you can add code after the </html> tag to clear the session if you like, for example:
<?php if(isset($_SESSION['WAVT_updatemember_Errors'])) unset($_SESSION['WAVT_updatemember_Errors']); ?>
it looks to me like you copied the validation show if code from the add member page to the update member page. The validation show if code cannot be copied from one page to another. the validation show if code is unique to each page. you need to apply the validation show behavior manually rather than copying the code.