Smoke resulting from fire (or fire itself) travels two blocks outward through nonflammable materials. Should this be happening?

What I expected to happen was...:
What should be happening is that it should contain the smoke and fire inside. The smoke should be contained in the chimney of my fireplace, as shown in bugpic1.png and bugpic2.png.

What actually happened was...:
What actually happened was the chimney caught fire outside, usually in the locations shown in bugpic3.png and bugpic4.png. It went through the brick.

Steps to Reproduce:
I'm not actually sure how you can reproduce this without me giving you an excessively large list of instructions, so I replicated a section of my house in a singleplayer creative flatmap. The mediafire is here: http://www.mediafire.com/?jcdggo9ap899ztn

I am 99% sure that this should not be happening, as I used this fireplace layout in previous Minecraft versions and it worked perfectly. This problem was discovered in a multiplayer survival world. This fireplace layout was used in previous Minecraft multiplayer server versions, where it worked flawlessly.