Vector data are tied to a certain terrain rendering level, and when you get far enough when that level vanishes, the roads go too. Larger vectors (large rivers, fields, runways) will be tied to a coarser terrain level in the future and they will stay longer, generally the level where the data are should be computed so that they disappear when going sub-pixel.
Currently the disappearance is more visible also because there's no procedural vector anti-aliasing on the roads yet.