10x30 is a 1:3 ratio. 512x2048 is a 1:4 ratio. As a result the texture will be stretched a bit since the ratios don't match. To get better lines, you'd have to waste some texture space by only using 3/4 of the uv space so the ratio is the same.
This happens in any application that I have tested it in. I can't figure out of its normal or not. Here is the scenario. I have a 512x2048 texture and a 10m x 30m polygon. I unwrap the polygon and then quantize it so that it fills then entire 0-1 UV space. This means the texture should be perfectly mapped to full texture…