Unable to add a category or a subcategory when editing a blog post

Steps to reproduce:

• Click on "Blog"
• Click on a blog post
• Click "Edit"
• Scroll to the bottom of the page and click on "Add a category"

You get an error on IE8 and on the other supported browsers nothing happens.

Some bullets appear for each category and for the "Add a category" button. When you hover over the list of categories the current field isn't highlighted and the tree icon doesn't appear.

You are able to manage the blog categories if you go to this page: http://localhost:8080/xwiki/bin/view/Blog/ManageCategories

Doesn't reproduce on 4.5.3. I've attached screenshots.