Controllers in sub-folders

[eluser]GSV Sleeper Service[/eluser]
this is puzzling me, I've put a controller in a sub-folder called 'maintain'
the controller is called 'Jobs', in this controller I have a method called 'detail' which takes one parameter ($job_id)

the detail method looks like this

Code:

function detail($job_id)
{
    echo "job_id = $job_id";
}

when I test this in my browser using http://domain.com/maintain/jobs/detail/123 I see on the screen

job_id = detail

WTF?! if it thinks detail is the parameter then how does CI know to use the detail method?