Hasta La Motion!

I have some trouble when i use the zBlur node. I try to control the depth between my front element and the others with my depth pass from the scanlineRender.
So i adjust the knob to have my front element sharp and my back blurred.
All is working except that i have a strange stroke around my front element.(i think it’s everywhere but not visible with the depth blur). It’s not a black or color stroke like in a wrong premult. It’s when my element is sharp there is not a smooth transition with the other elements (or cards).
I hope to be clear enough and will try to upload a screenshot of my problem
thanks for your answer
b