Conventions for indenting in comment hierarchy broken?

When comments in a threaded list are shown "oldest first," I found the second and subsequent comments to the original post shown as if they were comments to the first comment (or a later one). This occurs whether the list is expanded or collapsed. When the list is shown "newest first," the error doesn't occur--I thought. But when I created a new set of comments on another page, "oldest first" worked fine, and "newest first" was broken. And is the "flat" view displaying properly?

I attach a set of screen shots. The theme is Garland.