This one had caught me out on more than one occasion recently, and it relates to adding links to external websites to issues (Wiki posts) in the Redmine issue tracking system. The syntax used to cite links to other pages on the same site seems reasonably straightforward (and largely standard):
However, to insert a hyperlink to an external website, you need to do the following:
To be clear, you need to add double-quotes around the text, then insert a colon between the closing quotes and the hyper link (with no spaces in between). I kid you not!
Source: Redmine Wiki Formatting