URL rel attribute not set for broken URLs
Summary
There seems to be a minor bug where the rel attribute isn't set for some URLs in a Markdown field. I believe this has been abused by spammers in the past for PageRank / similar purposes. I don't believe there are immediate security implications, but you want want to consider fixing this nonetheless.
Steps to reproduce
Inspect the URLs above. You'll notice that the rel attribute is only set for the first URL.