I was playing in 1.8.9 and I accidentally opened my 1.12.2 world. The next time I loaded that world in 1.12, there were chunk errors across the area I had loaded in 1.8. Chunks had been duped and included the blocks I HAD ALREADY PLACED. So you could duplicate blocks by using this method. I think this is just the chunk dupe from ages ago but idk.
This is not a bug - Mojang does not support downgrading, ever, so any reports of world corruption as the result of loading a world in an older version will be considered invalid; for example:
Downgrading is not, was never and will never be officially supported!
They could have easily prevented this by simply disallowing the game from loading worlds created in a newer version, as is done on Bedrock, and as I've done in my own modded version, which was a simple matter of checking for a tag that is only present in worlds it creates (Java has stored a version NBT tag since 1.9 so they could have implemented the same thing back then. In my case, unsupported worlds do not even show up in the saves menu, you can only tell they exist because you can't create a new world with the name of an existing world):
public class Minecraft implements IPlayerUsage
{
// Used to identify worlds created by TMCW so only those worlds show up under saves; also used as
// the NBT tag for the diamond ender chest inventory (this is what is checked). TMCWv2-4 use
// "DiamondEnderChest"
public static final String VERSION_ID_STRING = "DEC5";
public class AnvilSaveConverterFix extends AnvilSaveConverter
{
public AnvilSaveConverterFix(File par1File)
{
super(par1File);
}
public List getSaveList() throws AnvilConverterException
{
if (this.savesDirectory != null && this.savesDirectory.exists() && this.savesDirectory.isDirectory())
{
ArrayList var1 = new ArrayList();
File[] var2 = this.savesDirectory.listFiles();
File[] var3 = var2;
int var4 = var2.length;
for (int var5 = 0; var5 < var4; ++var5)
{
File var6 = var3[var5];
if (var6.isDirectory())
{
String var7 = var6.getName();
WorldInfo var8 = this.getWorldInfo(var7);
// Removed support for pre-Anvil worlds (version 19132) as they can never have been
// created with TMCW
if (var8 != null && var8.getSaveVersion() == 19133)
{
NBTTagCompound player = var8.getPlayerNBTTagCompound();
// Only adds worlds created by TMCW to list of saves; hidden worlds will still
// prevent creating a new world with the same name. Checks for presence of
// diamond ender chest tag in player data (player is normally never null, in
// which case saves are visible).
if (player == null || player.hasKey(Minecraft.VERSION_ID_STRING))
{
boolean var9 = var8.getSaveVersion() != this.getSaveVersion();
String var10 = var8.getWorldName();
if (MathHelper.stringNullOrLengthZero(var10)) var10 = var7;
var1.add(new SaveFormatComparator(var7, var10, var8.getLastTimePlayed(), 0L, var8.getGameType(), var9, var8.isHardcoreModeEnabled(), var8.areCommandsAllowed()));
}
}
}
}
return var1;
}
else
{
throw new AnvilConverterException("Unable to read or access folder where game worlds are saved!");
}
}
}
Also, by downgrading from 1.12 to 1.8 you'll have wiped most if not all entities, including tile entities (such as chests), since they changed their names in 1.11, even if just to make them lowercase (e.g. "Chest" became "chest"; older versions are case-sensitive so they will have no idea what a "chest" is). All blocks, items, and entities not present in 1.8 will also have been removed so this is a very poor way to "duplicate" anything. Even worse things will happen if you go past 1.13 - all loaded chunks will be completely reset.
I was playing in 1.8.9 and I accidentally opened my 1.12.2 world. The next time I loaded that world in 1.12, there were chunk errors across the area I had loaded in 1.8. Chunks had been duped and included the blocks I HAD ALREADY PLACED. So you could duplicate blocks by using this method. I think this is just the chunk dupe from ages ago but idk.
This is not a bug - Mojang does not support downgrading, ever, so any reports of world corruption as the result of loading a world in an older version will be considered invalid; for example:
They could have easily prevented this by simply disallowing the game from loading worlds created in a newer version, as is done on Bedrock, and as I've done in my own modded version, which was a simple matter of checking for a tag that is only present in worlds it creates (Java has stored a version NBT tag since 1.9 so they could have implemented the same thing back then. In my case, unsupported worlds do not even show up in the saves menu, you can only tell they exist because you can't create a new world with the name of an existing world):
Also, by downgrading from 1.12 to 1.8 you'll have wiped most if not all entities, including tile entities (such as chests), since they changed their names in 1.11, even if just to make them lowercase (e.g. "Chest" became "chest"; older versions are case-sensitive so they will have no idea what a "chest" is). All blocks, items, and entities not present in 1.8 will also have been removed so this is a very poor way to "duplicate" anything. Even worse things will happen if you go past 1.13 - all loaded chunks will be completely reset.
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?
Thank you for explaining this to me