Submit buttons are missing everywhere if SimpleThingsFormSerializerBundle is in AppKernel

I just installed the bundle (dev-master) 

```
php composer.phar require simplethings/form-serializer-bundle dev-master
```

and added the bundle to AppKernel.php

```
new SimpleThings\FormSerializerBundle\SimpleThingsFormSerializerBundle(),
```

Then submit buttons on my forms disappear everywhere on my symfony2 app.
Any idea on what is happening ?

Symfony2 version: 2.6.4
