Furnace GUI looks a little off. The overlay for FUEL STATUS seems to be cut short. The GUI Texture holds a 14x14 Box to Overlay active fuel but only uses 14x13 of it (14 Wide, 13 High) resulting in the bottom line of the icon being cut off. I inverted the Overlay Section of the PNG to illustrate. If you look closely, the "Shadow" of the Flame is not inverted on the bottom (14th line).
Note : Down Graded to 1.7.2 and it is correct there. Also, switch to my Texture Pack and it was also cut off (as I use all 14x14 icon).