A map with a file size of 1 KB.

The map was created and weighs 51 KB, but it needs editing. After editing, the file weighs 1 KB. I saved it as a new file, overwrote the existing one, changed the name, and tried many other things – the result is 1 KB, and the map is 1 KB.

The "original" is still available. How can I properly save the edited version?

P.S. The original works normally (i.e., the game recognizes and launches it).

I don't remember how I managed to save it like that...