Why do @ tags only work some of the time?

You can @ tag any friend, or fan Page you’ve liked, or Event to which you’ve RSVP’d. However, depending on a few temporary bugs on Facebook and possibly browser issues, @ tags are not always 100% reliable. I’ve found clearing cache, restarting my browser, switching from Firefox to Safari or Chrome, or logging out of Facebook and back in again can help in getting @ tags to function properly. This goes for the new @ tags in comments too.