Changing seed generation

I was playing through the beta and going seed hunting, because that's something I enjoy - I even gave some seeds on Caves and Cliffs seed picker thread. Unfortunately my comments weren't approved to be published, and I think I figured out why - when I tried to load one of the seeds I suggested (and wanted to play), I got an entirely different world generation! I also noticed that the seed number had changed on the world file, so it went from -12137462591 (what I input) to 747439297.

Trying to get to the bottom of this problem, I loaded up an entirely new world/seed and took note of the immediate surroundings/structures:

-1143542928 Spawn in a Savannah biome
At -162, 93, 101: There is a tiered acaia village with neighbouring ruined portal

Loading up the very same seed in a new world, the seed number HAS remained the same - however the surroundings are now slightly different. Essentially, the village and portal relocated to -238, 74, 74 and has a different layout.

Not sure what exactly is causing this issue - I triple-checked and I have no mods on that should be interfering with this, nor the experimental features. Just pure vanilla beta!