5

This question contains ten links to other posts on the Stack Exchange network. On Meta Stack Exchange, bare links like these are replaced by the question titles. However, on that particular post, it stopped working after the fifth link:

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When you edit the post, you see in the preview that all links are rendered, even though it takes a while:

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This answer seems to imply that it's by design, since that post links to more than 5 different Stack Exchange sites. In that case, the markdown preview should exhibit the same behaviour.