When testing XamlPlayer on a GeForce GTX 590 3GB DDR3, I am seeing some strange artifacts at 8x and 16x MSAA. When I zoom in enough, or zoom out enough, these artifacts disappear. But they are present at the default size. Any idea what is going on?

The artifact is faint but there. If you can't see it you should zoom in on an image using a paint program.

There are MSAA artifacts on some Intel cards but this issue seems to be different.

Do you see the problem in other samples? Do you have the latest drivers?

I have attached you a xaml, could you test it and tell me if the artifacts are still visible? we are unable to repro that bug.

No I don't see the problems on other samples.
Yes I have the latest nVidia drivers.
The artifacts are not visible ont he XAML you provided.

We have added this bugs to the database. Thanks!