I think the Help page should make some mention of the different effect in the category namespace. — Robin Patterson(Talk) 01:52, January 1, 2010 (UTC)
I've made a brief mention in the notes section. Kirkburn (talk) 11:16, January 13, 2010 (UTC)
Pipes don't seem to work quite the same way inside the <poem> tags. If I put [[:Category:Foo|]] then the result is not Foo but [[Category:Foo|]]. The initial colon is elided, but the rest of the link becomes just text, not a hidden link, or even a link at all.