The Bug:

Sometimes when closing a world and creating a new one with a different seed, structures near the old world's spawn are generated in the new world exactly as they were in the old world.

Picture of the original village:

Picture of same village generated in another seed:

Picture of same village generated in another seed:

How to Reproduce

I had a difficult time trying to reproduce this bug but I managed to retrace my steps and find it happening again. The following steps are how I reproduced it, though there might be a way to shorten it:

1. Generate a world with seed 8607743678947408306 in an older version (I managed to reproduce it with 1.12 and 17w47b). There will be a village in the spawn chunks, at 132 86 55.
2. Close the game and open up the world in the latest version (18w06a).
3. Load the village's chunks.
4. Fly in any direction, making sure to generate new terrain (I flew for about a thousand blocks)
5. Close the world, and without exiting the game, generate a new world with any other seed ( Managed to reproduce both with 3239279967284580547 and -7985168147923234878)
6. Go to 132 86 55, and there should be the same village there. Although there are no villagers, /locate Village does find it. Generating the second world any other way will not spawn the village at that position.

EDIT:

I managed to reproduce this with another village in 18w06a without changing versions or closing the game; it was a matter of generating a new world with a village near spawn (same seed) and creating a new world, it's likely that the new world will contain one of the villages near the spawn of the first world.
Picture of the other village reproduced in seed -6302653602812631822: