This is an old issue that I mentioned before elsewhere (too much data so can't find it right now). Anyhow, it still searches through (all??) threads. I'm talking about the little "Search for" box at the bottom LHS corner. It used to (in distant past) only search within that thread that you are in. This was very useful for longer threads (imagine a 30-page long build thread and you only wanted to check the timber floor, for example)!
I am not talking about the Search located on top of the page (the one that has 'advanced search' link next to it). This search used to (and still does) search anywhere (and has the Advanced options) and there's no problem with it.
Now both these searches do the same (only there are no Advanced options for the bottom search) and you can't search within a single thread (other than going into each page and using standard browser search - time consuming for long posts).
Confused yet!??!