The DefaultTextRenderer does not recognize a valid issue key when it directly follows a URL on a previous line. For example, check out the change history of TST-21313
http://jira.atlassian.com/browse/TST-21313?page=com.atlassian.jira.plugin.system.issuetabpanels%3Achangehistory-tabpanel

I believe it's because when the renderer finds an issue key in the text then JiraKeyUtils works backwards looking for :/ to make sure the key isn't part of a hyperlink but it only stops if it encounters ' ' rather than stopping if a character matches /\s/