Restart your minecraft launcher. See if that helps. If that doesn't work If you have mods then remove them, If you don't have mods or it does not work Try to change options in Graphics If that doesn't work then Reinstall minecraft
(it could be me but) It looks like you are using 1.8, if you are, try using 1.7, that could be the problem sometimes.
This doesn't have to be a bug, it could be a high ranked staff member such as death or jerry or harry may have removed them by mistke. But if this is indeed a bug i suggest you remove any mods or testures pack or restart your micraft or realod the server. If that doesn't work you dont have to reinstall minecraft, but if it is that damaging then you should.