Since the list is re-loaded, the list plugin has to be re-initialized.
You can do this by manually updating the code that calls the plugin... you currently have:
framework_load_plugin_url('plugins/inc.pv.php',document.getElementById('registrazione_frm'),'pv','','');
You would need something like:
framework_load_plugin_url('plugins/inc.pv.php',document.getElementById('registrazione_frm'),'pv','','', bootstrapInit);
Then add this to the page somewhere:
<script>
function bootstrapInit() {
$('#punto_vendita_reg').selectpicker();
}
</script>