I've found the solution.
In edit_folder.inc file, row 124, I've insered before:
$select = rcmail_mailbox_select(array(
'name' => '_parent',
'noselection' => '---',
'realnames' => false,
'maxlength' => 150,
'unsubscribed' => true,
'skip_noinferiors' => true,
'exceptions' => $exceptions,
));
The following instruction:
array_push($exceptions,'#Public');
All the public folders are not inserted in combobox menu in parent folder selection, now.