Just updated to 6.11.08 and the first thing some people on my server observed was their burning boxes reigniting after they blocked the front with a solid block.
But they also stopped outputting heat.
Someone tried it with a glass block in front of it and the burning box still emitted fire particles (after the last fuel unit was fully consumed).
Also if the fuel was fully consumed, the boxes remained burning and automatically reignited new fuel afterwards.
I hope this was described in a understandable manner, just wrote this from descriptions I recieved.