Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here
I'm mining on lv5 just above bedrock and filling in lava pools to continue my strip mines and the blocks are going on fire beneath me on lv4, even when no lava blocks where present above below or around.
Bedrock, Cobblestone and stone will occasionaly catch fire while i'm standing on it and ignite me. i've died a few times because of it. I'm using signs to hold back the lava but It's happened when i've just used blocks and point and place. it's usualy a block below and behind the one by two corridor i'm working in. it goes out when i hit it or use water. but it is killing me a lot

What actually happened was...:
Describe what happened here

Steps to Reproduce:
1. fill in lava blocks on lv 5 or around, using just blocks or signs to hold back lava (i'm in a 1X2 strip mine corridor when this happens)
2. ...occasionaly blocks behind or under your feet will catch fire. including stone, cobblestone and Bedrock
3. ...the last instance of this happening had a torch above the square that went on fire