Chunks do not generate identically when regenerated.
Repeat by:
1. Recreate the same world.
Or:
2. Delete region files, and let them be regenerated.
Landscape is the same. Decorations (trees, plants, mushrooms, etc; sand on the floor of the ocean) are NOT the same.
Easiest way to see this is to look at the region file boundary in the ocean with a potion of night vision. However, I managed to find significant differences in plants near spawn when I re-created a test world.
Additional notes:
1.0 and 1.1: I could, and did, regenerate chunks and worlds without any problem. I thought I did the same in 125 as well.
I can confirm that changes happen in 164 and 174. Not sure about 147 (I know it does not match the 125 generation); did not test the 15x series.
Comments 2
Actually, it has.
I have repeatedly re-created the same world/seed in 1.1 through 125, using the trick of specifying generator version – http://www.minecraftforum.net/topic/1003941-howto-use-a-11-seed-in-12w03a-or-later/ – and I've had no issues with trees being changed in that range. So seeing this be very non-deterministic in 174 is a shock.
Additionally, I am saying that the layout of sand and dirt on the ocean floor is not consistent/deterministic. The vast majority of the time, yes, but it is still possible to get sharp boundary lines.
I know that chunk generation has two phases. Roughly, phase one is 100% deterministic and relies on no other chunks, and includes height (technically noise) and caves/ravines. Phase two is the decorations, including ores, trees and buildings, that can rely on other chunks existing (an ore deposit or tree can extend into adjacent chunks), and this phase can be changed by having different mods loaded, making different use of the RNG.
But when the game is not changed – and I'm talking about two tests of vanilla 174 with the same seed at spawn being different here – those decorations should still be identical.
Invalid
Tree generation is not bound to a seed/world. That has been like this forever.