I suspect it's because you've got problems with the case of the text you're checking. If you try

s/(a guide to )(.*)/$2 - $1/i
[download]

it seems to work ok for me, since the /i tells the regex to ignore case.

Hey, if there's code up ^^ there ^^, don't blame me if it doesn't work.

But today you took me walking, Through a land that we have lost,
While our children sit at websites, With no access to the cost