what glitch? That's not a bug, that's a feature: if a user deletes a comment other than the last one of the page, an empty entry stays.
Otherwise sometimes people seem to talk alone or a reply can be mis-interpreted because it does not apply any more to the same post as intended.

If the deleted comment was really useless and does not cause problem for the rest of the page, admins can delete them for good (I do that sometimes when noticing deleted comments).