I was disappointed to see that as well. That was the first lens that I bought after getting the D7K body and I immediately bought a cheap off-brand glass filter to put on it. So, I think it's the filter's fault. Most of my shooting is daytime so I never had a problem with it. After seeing that ghosting I have since put that thing in the trash.
I too have a cheap Tiffen, so maybe it is a cheap filter problem. Not a big enough problem for me to put it in the trash though.