Forge changes some block id's of minecraft. I use forge 10.12.1.1084 and I have no other mods installed.

 

edit:

I installed not enough items so I could see the block id's.

    link: https://dl.dropboxusercontent.com/s/zfrqxlku0j18gx2/sheet001.htm

how can I fix it so that it loads my 1.6.4 world correctly and not replaying air-blocks with stairs

No it is my survival world from 1.6.4.

It should give blocks the same IDs as vanilla, unless you're loading a broken world, then it tries to fix it.

Zip your MC folder and send it to me, I want to see what you've done to break it so hard.

It should give blocks the same IDs as vanilla, unless you're loading a broken world, then it tries to fix it.

Zip your MC folder and send it to me, I want to see what you've done to break it so hard.

 

I Ziped my whole .minecraft folder, but only my "mods world" I had trouble with. I know that some mods in my save are not updated yet but I was trying to update my world with the mods that already were updated.

PS: I already tried to load the world with no mods installed.

 

download: https://www.dropbox.com/s/6razoyokaksf2ed/minecraft.rar

Interesting, not sure what to say dude, your world's data is massivly fubared. I can work on trying to figure it out. But 3/4ths of your mods 1.6.4 mods do not have the metadata needed to update correctly so Forge tries to assume things. But i'll see if I can figure out what has corrupted the data, but I make no promises your world may have to stay on 1.6.4.

OK thanks for your help guys

I loaded my world with forge 10.12.1.1079 and without Buildcraft and the world loaded correctly!!