EDIT: Never mind, just went over the patch notes and it says that it was a bug that is now fixed. Kinda sucks, I always wanted a giant fireplace but seems like there will be a giant empty spot in my base now. 
 
Let me say first that I've never made a fireplace before, so this may be just be my noobiness. 
 
Anyway, of all the video's I've seen of people making fireplaces is them just setting fire to a log and it burns infinitely. When I try it though, the log burns for a few seconds and then disappears. Is it something new in a patch?

Lava works similarly, however unlike the infinite burning log, it has a much stronger propensity to spread (as my terribly posh library learned the hard way).

Use Netherock (the red coloured stuff) from the Nether which burns forever.

" Use Netherock (the red coloured stuff) from the Nether which burns forever. "