I'm afraid I don't know the reason myself. Sometimes it works for me, and sometimes it doesn't. Today I got lucky. :)
Originally I thought it might be something to do with the browsers. But it can't be that, since it works sometimes and sometimes not. There's probably a code bug. All I know is, when the search function is not working, it gives you the message that your 'message has been posted' as though you had written a post.