ThatDarnWinner

Yes, Optifine was the problem, turns out they made a new patch to patch this. Thanks, y'all.

Actually, Optifine was fine with chests before I added betterfps so I think better fps is the problem. I'll test.

Fixed. I can now fiddle with tile entities as normal. But I heavily rely on Optifine, so is it maybe due to this version of it being glitched? What is recommended here now?

A mb of a screenshot png of my mods folder, and the fml log, coming up! fml-client-latest.log

I play in any world on Forge with my selection of mods. I had to turn on an option in Forge's config that removes the tile entities if they misbehave, they always do. That config option also removes the entities if I place or break a block. They aren't totally removed but become translucent. The moment I look at one and it's highlighted by the grey grid thingy, my FPS drops from 110 to 0.5. I don't know how I'm gonna store my stuff. I will hand over my list of mods if asked for. And anything else.