Categories field updates (check / uncheck) are not taken into account after adding a new category when editing a blog post

Steps to reproduce :

1. Edit a blog post
2. Click on 'Add new category', fill in the category name and click on 'Add'

You will loose all the previous checks and after saving the document all the modifications of type check and uncheck made on the category list will be lost.

This is happening because the service handling the action of adding a category returns a list of malformed input names, for example :

<input type="checkbox" value="Blog.newCategory" name="Blog.BlogPostClass<ins>category">

while the correct name of the input should be in Blog.BlogPostClass_0_category.