[Mirroring]set direction in code receives compiling error,however direction attribute can set inside mxml tag

Steps to reproduce:
1. compile test file, there is a subTitleWindow component set direction in tag, as well in code.

Actual Results:
receive compiling error:
Error: Access of possibly undefined property direction through a reference with static type TitleWindowWithContent1.

<s:Button label="update to ltr" click="this.layoutDirection='ltr';this.direction='ltr';"/>

Expected Results:
no such error.

Workaround (if any):