Finalement forcer ini_set('arg_separator.output', '&'); n'est pas une bonne idée...

library/ZendAfi/View/Helper/TagPreview.php

@@ -21,7 +21,7 @@
 class ZendAfi_View_Helper_TagPreview extends ZendAfi_View_Helper_BaseHelper {
 	public function tagPreview($url, $libelle) {
 		return 					
-			'<a data-prettyphoto="true" href="'.$url.'?'.http_build_query(['iframe' => 'true', 'width' => '95%', 'height' => '95%']).'" title="'.$libelle.'">
+			'<a data-prettyphoto="true" href="'.$url.'?'.http_build_query(['iframe' => 'true', 'width' => '95%', 'height' => '95%'], '', '&amp;').'" title="'.$libelle.'">
 					<img
 					   src="'.URL_ADMIN_IMG.'picto/show.gif" 
 					   title="'.$libelle.'"

library/startup.php

@@ -26,8 +26,6 @@ if (!function_exists('xdebug_break')) {
 
 
 function setupOpac() {
-	ini_set('arg_separator.output', '&');
-
 	Zend_Loader::registerAutoload();
 	setupConstants();
 	require_once('requires.php');