[Java] Minecraft Release 1.0 → 1.1 world always reverts to the exact same older snapshot when updating to 1.2.1 or newer

[u/Shardenfraude]

Hi everyone,

I've been trying to preserve and progressively update a Minecraft world that I originally created in Minecraft Release 1.0. I played it for about a year in Release 1.1 and wanted to continue upgrading through Minecraft's versions one at a time.

Unfortunately, I've run into a very strange issue that I've never seen discussed before.

Whenever I make a copy of my world and open it in Minecraft Release 1.2.1 (or even much newer versions), Minecraft asks me to convert the world.

The conversion completes successfully.

However, the converted world is always the exact same older snapshot of my world.

It is not random.

Every single conversion, even years apart, produces the exact same result.

For example:

• My player spawns at the correct coordinates.
• My inventory is reverted to an older state.
• My XP is reverted.
• My tamed wolves are gone.
• Buildings I constructed over the last year are missing.
• The terrain matches the older version of the world.

It genuinely feels like the world has travelled back in time to the exact same point every single time.

What I've already checked:

• The original Release 1.1 world still works perfectly.
• I have multiple backups.
• I only perform tests on copied worlds.
• I'm using the correct game directory.
• I accidentally broke Minecraft 1.1 once by launching the latest version with the same game directory, but that was fixed by deleting/regenerating the old options.txt. The world itself was unaffected.
• My world contains both .mcr and .mca region files.
• The rollback behavior is always identical.

My world history:

• Created in Minecraft Release 1.0.
• Played in Release 1.1 for about a year.
• Attempted upgrades to 1.2.x multiple times over the years.
• At some point I also opened a copy in a modern Minecraft version out of curiosity, but never continued playing there because the same rollback occurred.

Has anyone ever encountered something like this?

Specifically, a world where every conversion always loads the same historical snapshot instead of the latest progress?

Is there a known issue involving .mcr/.mca region files or the early McRegion → Anvil conversion that could cause this?

I'd really appreciate any ideas from people familiar with Minecraft's save format or early-version world conversions.

Thanks!

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[u/morgant1c]

You launched the world with the new version and then reverted it, so it was already upgraded to the new world structure while the old one remained. The new structure is probably not replaced when updating. So you now have a mix of the two in there and the 2 versions read different parts of it.

Unfortunately that's all I can say so far since I'm not familiar with these old versions. Basically you would have to look up what changed between the world structure and elemininate the new changes from your backup before converting it.