Submit buttons are missing everywhere if SimpleThingsFormSerializerBundle is in AppKernel

[bellecp]

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