Hi,
Thanks for your message. This one isn't a bug, the translation settings have always worked in world coordinates (it's the same in normal scatter mode as well). There is a workaround though. You can use a Forest Effect called X/Y Local Translate that allows you to randomise the position in local coordinates. It also uses scene units instead of percentages which many people find useful.
It's included with Forest Pack, but I've attached you sample scene with it applied so you can see how it works.
I hope that helps,
Paul