I built a house next to a lava pit but made sure to cover the entire pit with dirt so it wouldn't burn my house down. Afterwards I went exploring a nearby cave and when I came back part of my house burned down.
What I expected to happen was, after I covered the lava pit with dirt, that it wouldn't burn my house down
What actually happened was it burned my house down
1. Build a house next to a lava pit.
2. Cover the pit with dirt.
3. Walk 100 or more blocks away for 15-30 minutes and come back.
It's a known quirk in Minecraft that fire and lava will burn any flammable block up to two blocks away and five blocks above, regardless of how many solid blocks are in-between. Is this the issue you're seeing, or something new?