`onKeyDown` bug fix (#5766)

+ close #5487

components/auto-complete/index.tsx

@@ -52,7 +52,14 @@ export default class AutoComplete extends React.Component<AutoCompleteProps, any
     const element = children && React.isValidElement(children) && children.type !== Option ?
       React.Children.only(this.props.children) :
       <Input/>;
-    return <InputElement className="ant-input">{element}</InputElement>;
+    return (
+    <InputElement
+      {...element.props}
+      className={classNames('ant-input', element.props.className)}
+    >
+      {element}
+    </InputElement>
+    );
   }
 
   render() {