In HTML, a Return is treated as a space, and a string of spaces reduces to a single space. You have ro use <p> or <br /> to create a line break.
In Wikitext, a double Return creates a paragraph break.
What you had here was a Return, then some spaces, then another Return. This looks the same as a double Return, but it doesn't work the same. It just reduces to a space. The blank line has to be empty.