Good catch! It's part of the not-yet-written incremental-update logic: we want to be able to automatically find the files whose current version is not yet in the index, write a new segment for them, and possibly merge some segments to keep the number of segments under control. I'm not sure if incremental updates will make it in—in large part, that depends on whether you and other reviewers would be willing to look at such substantial new functionality in code you've already reviewed once.