My friends and I play in a shared world hosted on Thorsson's PC. Initially we did a lot of exploring, but stopped after we found Deep North and South so we would not mess up future biome updates. But we left a portal in each.

Just before the Mistlands update dropped we moved our Mistland portal back out into an older biome. Last Friday I had to go to that portal to take a boat and rescue a couple of our explorers. I appeared but there was no portal or crafting table! And I was standing on top of one of those tall undulating hills of the Mistland - our Mistlands had grown and spread into the area formerly in the older biome.

A few seconds later I heard construction break and the parts of the portal and the crafting table popped up on the surface of the land.

Just thought it was interesting that the updated biome spread out beyond its original footprint and that it buried some of our construction...