Sounds like typical textile margins of error to me. I've had that happen with jeans before, same size, same manufacturer, but different model, and one is larger/shorter than the other.
To help solve the chamois problem you are having, I wear good-fitting chamois shorts under non-chamois tights/bib tights.
Last edited by jfowler85; 11-04-15 at 01:25 PM.