That's pretty annoying. Though I think I found a workaround: one-word searches work (at least for me). Do a one-word search first, then do a multi-word search on the page that comes up. That works for me at least.
For me, my solution is just to go to any post it thread with a tag and click on the tag. That leads to the search page and it shows every post with those tags. Remove the tag and type what you want to search and voila, works like magic.