Observed behaviour:

I run a personal minecraft server on my private computer. Once, power shut off for a few seconds resulting in the computer shutting down with no warning. After I restarted the computer and the minecraft server, I noticed that several chunks in the areas loaded by online players have been reset to their newly-generated state. This means that all player-built structures were erased. Entities (like item frames) seemed to be unaffected.

Expected behaviour:

The server should make use of an advanced saving strategy so that, in case of a spontaneous power shut down, the server can revert to an older save (a few seconds or minutes) instead of re-generating the unsaved/corrupted chunks.

Note:

I also noticed, that a similar corruption glitch occured when I tried to copy the world while the server is running (this was an experiment, and not done on a production system ).

Conclusion:

Chunks get corrupted when the server fails to close file I/O. There should be a system in place to prevent that.