Chunk gets completely reset when it has blocks outside of the currently allowed dimension height/size

I was using the caves and cliffs preview pack and my idea was that i can put blocks under the world with the pack then remove it so i have blocks under the world but when i did it i re-joined to the entire chunk got a reset and i know that Minecraft updates don't touch old chunks because of builds. 
I hope this gets fixed because it reset a chunk near my base with a crater  i made so i have a mine.

Thanks for reading this.