Slice Tool imprecision

Hi,

we have quite big problem with Slice Tool in Illustrator CS6.

We have simple curve then slice is created from Object - Slice - Make so the slice is exactly fit on the object. At least on the artboard.

But when we want to export that object-slice for the web, there is a one pixel space between one edge and curve (which is exactly horizontal at this edge).

This is the slice on artboard, there is no visible imprecision:

Same but magnified:

Here is the same slice in Save for Web dialog, there is visible space which is then on the output image:

Can you tell us where can be a problem or is it a bug? How can we solve it?

Thank you very much.

Jiri Formanek