When taking 480p or 512p video that you then line double (960p and 1024p respectively), there are too many scanlines. Basically it appears there’s maybe double the amount of scanlines, and they’re thinner. However, a 240p signal of the same game still has correct scanlines at 4x (960p).
Here’s pictures I took to show how all the other modes appear to be fine: Imgur album
I kept the scanline intensity the same on all the pictures taken.
I don’t know if this potentially affects other modes such as 480i line 4x’ed to 960p (I think you can do that). I haven’t done much testing on interlaced signals.