1. Open the provided project
2. Browse for the level.dat file in Assets-->SamOatesGames --> UnityMineCraft --> Examples --> Flat World
3. Right click on level.dat and reimport the asset

Result
An error message appears in the console:
"UnloadUnusedAssets incorrect caused some assets to load. This can easily cause deadlocks or crashes."

Note:
The scriptedImporter is creating a new scene upon import and this is probably what causes the error to appear.

Note on why this is being resolved as "won't fix": scenes are application state constructs that at the moment and are not treated as actual assets: there is no Scene Asset type and in the context of an importer, scene don't make sense since they cannot be the output of a scripted import event and when creating a scene it actually alters the global state of the application which violates what importers are allowed to do.