How interesting! I've tried to reproduce this by doing "reply with quote" on some posts that contain a link, but no success so far. I'll let you know if I find the cause.
All I can suggest is that people try to remember to preview posts before posting the final version. I always "go advanced" on the Web to check the post before submitting - I'm not sure how that works on the mobile site or Tapatalk. If you do preview, any issues (like the "link breaks thread" issue) will show up.
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