See Bug #690355 for a sample file and more details.
Why do we even want the x11 device to honour #copies? I'd think in a viewing context once would be enough.
It's the behaviour the user who reported Bug #690355 expects, though I agree with your comment.
I read that as a data point rather than a change request. I think Till was trying to pin down where the number of copies function was implemented. I don't believe it's appropriate to interpret /#copies or NumCopies literally in a display device like the x11 devices.