What hilariousetc said above ^
Someone already asked the same thing before and that's what I answered:
I can't barely even understand what does it seem supposed to "Select no more than 5 boards at a time". I'm having a hard time figuring out on this, it does hard to search on bitcoin's search engine. I can't find topics which I was lost to read, and now I wanted to read them again
They need to fix this soon out.
It's not that hard to understand. When you try to search on the front page, you are searching on all boards of the forum.
For example, try to open the "Economics" board and do a search there. You will only be searching on 2 boards (the board you are and their Child Boards)