Automaticly generated "hidden lines." Why?

[Sorceress21]

I often find myself dealing with SU automatically generating "hidden lines" on properly squared faces after I do an intersect. Does anyone know why this happens? Is it a bug or is this supposed to occur? It drives me crazy as it causes "unsoftened" areas to appear especially on curved faces. For those that don't know a "hidden line" is different than a "softened" line. A softened line is a longer dash pattern then hidden lines.

[jeff hammond]

it's because your faces aren't actually co-planar as you think they are.. if you upload a model showing this behavior (or portion of said model), i or someone else can point out the cause..

[thomthom]

I see that from time to time when I'm working on imported geometry - it appear to be some small inaccuracy issue which compound eventually to problematic inaccuracy.