--- a/management/univention-portal/www/PortalGallery.js	
+++ a/management/univention-portal/www/PortalGallery.js	
@@ -202,6 +202,7 @@ define([
 		},
 
 		insertDndData: function(data) {
+			this.dndSource.externalDropMap = {}; // Reset externalDropMap. see Bug #46666
 			this.dndSource.store.setData(data);
 			this.dndSource.insertNodes(false, this.dndSource.store.query());
 		},