I'm not sure if this have been posted in 1.4 or not but...
sometimes, when I'm playing in a server, the framerate goes as low as 20-40 fps. Fps went from 56 to 40 in the same map I was spectating. It also gets pretty low when I'm playing in the server too, as well.
Even if I play offline, the fps gets low occasionally as well.
I've asked other fellow players in the same server about this and they all agreed their fps was low as well.