The best time to register for DrupalCon Dublin is now. Earlybird discounts end July 29.
File list don't save state after form submit, if some fields of form not passed validation, in form with error messages file list will flushed.
Files should be uploaded by then, so it is not logical to still have files in Plupload. Module implementing this form should take care about saving files in $form_state and possibly displaying them as uploaded files.
Drupal is a registered trademark of Dries Buytaert.