Attempting to interact with the top face of blocks placed at the max build height gives the "Height limit for building is 256 blocks" message, and the action will fail. This affects things such as opening containers, placing minecarts on tracks, placing the top half of a slab (from the top of the bottom slab), etc... Again, take note that this only affects interactions from the top. Interactions from the side or bottom work just fine.

I first found this when I was building a drowned farm in survival. I was building the roof out of slabs (to prevent mobs from spawning) at the top of the world, and I noticed that when I accidentally placed another slab on the top half, it would immediately disappear and give the height limit message. However, I could place the top slab first, and fill in the bottom one afterwards.

What I expected to happen:

I expected that placing the top half of the slab would work just fine, and that I would have to deal with the double slab.

What happened:

The top slab immediately disappeared an I got the message "Height limit for building is 256 blocks".

I later went into a creative world and tested this. I found that the issue also affected snow layers, putting eye of ender in the end portal frames, and using bonemeal on crops. At first I assumed that this was an issue with manually increasing the height of a block's bounding box when it is at the top of the world, And I initially sent in this bug report as that. However, after a little bit more testing, I realized that this was incorrect. The real issue was that I was interacting with these from the top face, and that I could do the formerly impossible actions by instead interacting with the side of the block (in the case of the end portal frames and the crops) or the side of another block (in the case of the slabs and snow layers). A little bit more testing and I uncovered what I believe to be the root of my initial issues, and what this bug report is currently submitted as.

I believe that this is a side effect from the way the max build height is implemented into the game. It appears that it set to fail all interaction with the top faces of blocks at the top of the world, and this causes many interactions that should be legitimate (like opening a chest) to not function.