MAGETWO-71916: Fix for "flying" submenu in MassAction dropdown with large number of elements #10651

Author: Oleksii Korshenko

app/design/adminhtml/Magento/backend/web/css/source/actions/_actions-select.less

@@ -108,6 +108,10 @@
             min-width: 100%;
             position: static;
 
+            ._parent._visible {
+                position: relative;
+            }
+
             .action-submenu {
                 position: absolute;
             }