Nodecomment Thread bug- nodes aren't threaded correctly

I'm using the 'node comments threaded' view style to display comments. This appears to work at first. It correctly indents all of the comments and their children. However, it seems to order comments in a purely chronological order-- child comments aren't grouped with their parents. See attached image.

In the image, comment #5 is a comment on comment #1. It should be grouped underneath of comment#1 and should therefore appear before comment #4.

Has anyone else experienced this problem? I'm also attaching an export of the nodecomment view.

Thanks!