Type the following as a WordPress comment and see the fun:
This is www.yahoo.com link

This should ideally cause the whole phrase (This is www.yahoo.com link) to be hyperlinked and pointing to google.com. Unfortunately WordPress sees it as two links and a plain word:

  1. "This is" is hyperlinked to www.google.com
  2. "www.yahoo.com" is hyperlinked to www.yahoo.com
  3. "link" is not hyperlinked at all

Did you read about the other hyperlinking defect?