Apparently this is legal markdown, though unusual syntax for a link:
[Branchable](http://www.branchable.com/ "Ikiwiki hosting")
If that is put on a translatable page, the translations display it not as a link, but as plain text.
Probably a po4a bug, but I don't see the bug clearly in the gernerated po file:
"This was posted automatically by [Branchable](http://www.branchable.com/ " "\"Ikiwiki hosting\") when I signed up."
I cannot reproduce this on my Squeeze system with ikiwiki Git code; both the page in the master language and translation pages perfectly display the link (and tooltip) in my testing environment. Were you using an oldest po4a, such as Lenny's one? --intrigeri