Board Thread:Bug Reports/@comment-27200931-20170213123546/@comment-25330335-20170216030014

It must be something to do with how the spawner stores the data in the pyramid banner. I'll lay out my understanding of how spawning works, but first we need to understand a few things.

Minecraft renders each chunk only once, and only re-renders it if a block in that chunk changes. One chunk is not particularly time-consuming to re-render, so regularly placing blocks doesn't lag out your game. However, each chunk is only 16 blocks square.


 * 1) The spawner first edits the world so that the pyramid exists in the world files.
 * 2) Minecraft detects this change and attempts to render these changes (I'd like for someone to do the exact math for the maximum number of chunks that need to be re-rendered to spawn a pyramid. Since I haven't, it's a lot). This is the slowdown you experience.
 * 3) This slowdown basically halts the spawner's processes in their tracks, since the spawner task is running at a higher level than the rendering tasks.
 * 4) This means that any data that the spawner is going to transfer to any blocks that are a part of the structure doesn't get transferred until the rendering is done.

If all that is true (I don't actually know, I just made up a plausible solution using a few things that I know from Mevans), then that means that if you interrupt the rendering process by closing the world, it stops all the processes running in this world. That includes the spawner processes, and therefore the data the spawner gives the banner never gets there.

In all honesty, I don't see any feasible workaround to this one. For the most part, this bug won't be a problem in survival mode, so in creative, you just have to deal with it.