Damon,
Import the video and drop it on the "New Item" button to create a sequence that matches the source. Anything else is probably asking for trouble.
Then, I suggest you merely change the 1919 to 1896. That should make your second number divisible by 8 also - I hope. My best guess is that you might be able to get 1896X1000. Both 1896 and 1000 are evenly divisible by 8. (Jim is correct about that, of course. The whole thing falls apart if both numbers are not evenly divisible by 8.)
See if that changes things.
Now, I found something interesting. I downloaded a couple of RED clips. One was 4096X2304 and the other was 4480X1920. The first one produced sequence settings with preview files of 1920X1080. I like that just fine. The second one gave me 1918X822. Interesting. And I guess we know what your 4096 x 2160 does.
I looked for black lines after rendering the one with previews of 1918X822. I couldn't spot them. So I can't check to see what happens if you change it to 1896. Please give it a try and let us know if that helps.
-- Steven
