This issue has no crash log attached to it, as it is not a crashing issue. Railcraft has a block, known as block.hidden in the config and named Residual Heat in game, this block spawn all over our world.

Once spawned it is completely invisible and you cannot interract with it, however if it spawns over the ground, I cannot use a hoe on it anymore, if it spawns inside a tinkers construct smeltery the smeltery cannot be used anymore.

We found this block by using world edit in a MCPC+ server (the //distr command shows the presence of the block and the ID, tracking that back through the config gave us this block.hidden block)

Anyway, the block blocks a lot of interaction in the world by simply being there and has to be replace by for example dirt to remove it.

The issue also directly affects portal and fire creation, pistons are having hard time pushing when there is the hidden block blocking. Not to mention the more harder to detect plausible issues with farmable items such as sugarcane etc... basicly anything that relies there being an airblock.

I have also got this issue. I noticed it when one of my clients attempted to make a piston door.
I attempted removing it in MCEdit but to no avail.

Yep this thing is messing up almost everything on my server, from vanilla pistons to Tinker's Construct materials/crafted items. Not a good way to implement an aura...if you're going to do it, it needs to be an entity/tileentity, not a block.

These are bugs with Forge, please submit them there.