You're actually not missing the 'f', you're missing a little 'x' or check mark that appears after you click the "Like" button. The 'f' only appears when the user hasn't Like'd the page.
Can you test again, and reload the page once or twice, to make sure of the behavior you're seeing. Not sure why the check wouldn't show, but we can look into it more if it doesn't come back (may just be a temporary glitch with FB too).
Thanks,
Alex