Index: wp-admin/includes/list-table-users.php
===================================================================
--- wp-admin/includes/list-table-users.php	(revision 16009)
+++ wp-admin/includes/list-table-users.php	(working copy)
@@ -265,7 +265,9 @@
 					break;
 				default:
 					$r .= "<td $attributes>";
-					$r .= apply_filters( 'manage_users_custom_column', '', $column_name, $user_object->ID );
+					ob_start();
+					do_action( 'manage_users_custom_column', $column_name, $user_object->ID );
+					$r .= ob_get_clean();
 					$r .= "</td>";
 			}
 		}