Most probable reason would be that I ended up editing on the wrong machine while being offline or having it open on another one, so user error. But I don't know.
File locks or attempting to overwrite and open database would be a problem regardless of schema format or what application is holding the database file open for writing. This should be expected behavior and one would hope the app would detect this and seqfault / core dump without corrupting the original / previous version of the database file.