I played two Hot Spots with my Wizard and put them under the Beech Tree, when it came time for it to take damage, it only took 8 fire instead of 16, what gives?
You can only take damage from one terrain square per turn. I can't remember where I read that but it is not a bug it is working as intended.
Being able to deal 40 points of lava damage in one turn on huge enemies was deemed too strong, so it was nerfed. I say 40 because I don't remember if the terrain limit came before the lava damage nerf (it used to be 10 damage per tile), but it was 40 damage in it's prime.
Terrain attachments actually overwrite each other, a tile can never contain more than one attachment. This can be used for defensive purposes as well. For example, if one of your characters is trapped on lava terrain, you could use an Acid Blast to turn it into acid terrain, thus reducing the damage that character will take. This is what also makes Smoke Bomb so useful; apart from blocking LoS, you can negate huge swaths of terrain attachments with it (like those annoying mud patches). EDIT: Nevermind, I didn't actually look at the screenshot before posting this...
