Why isn't the code block formatted correctly in this answer?

Question

The very first thing in this answer to a Ruby question is a code block, but it's displaying as prose. But if you click "edit" to fix it, the code block displays properly in the preview pane!

It appears to be formatted properly as a code block (indented 4 spaces) and the indent uses regular old space characters ($20). There aren't any backticks or other unusual characters in it. Why is this not displaying as code?

[All the other "why doesn't this code display properly" answers I could find in meta have to do with code blocks appearing after a list (which isn't the case here).]

Answer 1

Caching. The post is quite old, and probably predates a rendering bug; the rendered output is cached and shown until the post is edited again.

I added a space, saved it and now it renders correctly.