The driver is misinterpreting the EDID data. See this thread
started by another fellow and then continued by me where we were first misunderstood and subsequently ignored. Fortunately, we found a workaround without any help from Nvidia.
Either that or you are just the 97th person to have an RPTV that just 'happens' to send the wrong 1080i EDID data to the driver...
I have my tv working at 1080i now using a ridiculous modeline that shouldn't work in a million years, but somehow does because I was able to find enough switches to make the driver ignore the fact that it's twice the frequency any 1080i tv should accept.