Permalink issues – 404 for single posts…

Not using a custom post type (just the built-in WordPress post type). Here’s the structure:

/blog/[category_parent]/[category_child]/[post]/

In Settings -> Permalinks, custom structure is set to: /blog/%category%/%postname%/.
Also in Settings -> Permalinks, category base is set to blog.
With the above setup, the only thing that doesn’t work is the actual post itself… It displays a 404 page. For example:

Parent category: hello
Child category: goodbye
Post permalink: this-is-a-test
Final URL: /blog/hello/goodbye/this-is-a-test/
Result: 404

I’ve tried a number of different permalink configurations, but I can either get it to where everything but the post loads, or I can get it to where everything but category pagination works…