Diffuse pass problem

Support Compositing and Post Processing
1

Hi. In the node editor when I want to put a antialiased object over a background I use “alpha over” node with premul enabled, it works fine (witout artifacts around the borders) when I use the whole image, the combination of all passes . But when I want to put only the diffuse pass over a background artifacts apper even with multiplying alpha in advance.

2

here is the blend file
http://www.sendspace.com/file/5i1960

3

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4

Thanks, I have found a another way, I use a combined channel “image” with very low specularity settings on my materials instead a diffuse channel, and when I need some specularity I use a color mix node set to add with a very high factor.