Error: Attempted to handle event 'becameInvalid' while in state root.loaded.created.invalid

I'm trying to make a form field validation system. When the focus-out event is triggered by the component, it adds a fake error. Here's my jsbin.

If you type something on the textarea and then focus out, it will add the "fake error" as expected. However if you do it again, it will raise the following error:

Error: Attempted to handle event 'becameInvalid' on <App.Book:ember418:null> while in state root.loaded.created.invalid.

I notice It worked well until I switched ember-data from 1.13.6. to 1.13.7. So if you want to see the JSBIN working without error, switch ember-data to 1.13.6.

I would like to know if I'm doing something wrong.
Thanks for helping!