Bulk edit doesn't play nicely with categories:

• chapters aren't collapsed into the category display on the front end when a category is added via the bulk editor
• I can add categories by bulk editing chapters, but I can't remove categories via bulk edit
• a category that is applied isn't always visibly selected in the bulk edit interface (even when the category is visible in the chapter itself)

Some other notes/suggestions:

• in the list of chapter posts, it could be helpful if any relevant categories were visible in a column beside the chapter name (it might also help to allow users to filter the list of chapters by category)
• it's not possible to add multiple categories to a chapter — there may not be a use case for this in reality, but I found it unclear based on the interface design