Every post is associated with a thread title. So this post is associated with the title "Search not working". If I search for posts by me with search title's only turned on and search for "Search" then it'll bring this thread up. This allows users to find posts based on thread titles they've posted in rather than the content they posted.
There is no way to search for first posts by you with thread title keywords.
In other words, search is working as designed, and it's not designed to help you with your specific search.
You might have better luck searching for the contents you posted in that first post, but if the title isn't particularly unique then you may be out of luck.
Also, Google does a great job of synonyms so if you remember the idea of the title but not the exact wording a google search for the title, your username, and "site:halforums.com" should search only this site and should produce very relevant results, much better than the internal search engine.