The attached file is a world region .mca modified by a map editor in development - so we consider the result a broken .mca

When we use this file in a vanilla server:

Observed behavior:
World starts but the region appears to have been regenerated as if there was no file there.
Any changes done in the world persists as long as the server is running.
Once the server is restarted the region is regenerated again, all changes done are lost.

Expected behavior:
Error message about damaged file.
File completely overwritten with the regenerated region.