I see. No, they are definitely not related

If you want to look at the post composition in detail:
  • Each post is a table
  • Each post table is divided into three rows, the top row has the time and post number, the middle row is the post content, and the bottom has the online details, rep link, warn link, and quote/quick reply buttons.
  • The middle section is divided into two columns, left part has the avatar etc., and the right has the post content:
    • A <div> area which contains the post title
    • A horizontal separator
    • <div> containing the post content
    • <div> containing the signature

Since the post content and signature are all lumped in together the browser treats them as one block of text. In deciding on a vertical size for the table, it has to fit both the left part (avatar etc.) and the right part (post + sig). Whichever is smaller will therefore have extra spacing at the bottom, so that the row is rectangular.