Thanks again for your bug report! I managed to find and ATI card where I could reproduce this and just released Patch 1, Candidate 3 which at least works on the test machine. For those who are interested in the technical details, here's what I found:
When antialiasing is disabled, you can render to a Direct3D surface created with the D3DXCreateTexture and GetSurfaceLevel commands. When antialiasing is turned on, my nVidia card has rendering artifacts unless it's rendering to a surface created with the CreateRenderTarget function. The only way I've found to treat this surface as a texture in later render stages is to also create a texture with D3DXCreateTexture and use StretchRect to copy from the render target to the texture.
Unfortunately, trying to create a multisampled render target with a floating point format fails on the ATI Radeon. But using the standard texture works without any artifacts.
My solution: When antialiasing is turned on, try to create the target surface with CreateRenderTarget. If this fails, revert to the standard D3DXCreateTexture function.
Now hopefully, it works for everyone.