cairo-dock with desktop effects has border with shadow

[ic3man5]

Compiz seems to be adding a border around cairo-dock and I'm not really sure how to stop it from doing so. See the attachment to see what i'm talking about.

[ic3man5]

bump

[fabounet]

maybe it's not compiz but the window decorator (like Emerald) ?
anyway there should be some options to tweak the shadows either in Compiz or in Emerald.