Not sure what triggers it, and only occurs every now and again (and easy to workaround), but thought I'd mention it...
It happens when you start typing to run a search, most often from one of the other views (start typing when in filtered search), but I think I've also seen it when already in title search but with a blank search box; you can only type one letter (I think it's usually a 't' or an 'a' but could be others, can't remember), then it won't accept any more input to the search box. You can delete the one letter you've put in, but then you can't type anything into the search box at all.
Fixing it is easy, you just alt-tab away from the program, then back again, and you can type normally; not a big problem at all, just odd
Thanks,