HP doesnt say how or why it would effect service. What we can surmise is that if it is not pinned out in the fax machine because of penny additional cost and most of the time it is not . Even though the second pr (o/w or y/bk) need not be used, it is usually terminated thus adding the possibility of acting as an influence to rfi or emf/emi. In my experience i just havent seen five foot of cord generating a trouble as your describing. But i do find this basic trouble interesting. Try the cord in another telephone to see it is any good. Then do as i do and cut it in half so there is no chance of reuse. Ill still put my money on a bad cord or poorly seated plug/jack.
