I took off the top rail and checked the spring--it seems that the spring is what is moving back and forth on both the short and long string sides. The loops that are not knotted seem to be holding tight and not slipping. My guess is that the shorter string just started out shorter. I've got the strings coming out at the bottom correctly--so maybe it will work when I hang it.
Getting the tension right is a bear--or at least it was the last time I took it down and rehung it. Basically, I like the shades--think they work very well and I like the two options for privacy. I don't like the metal blinds on the back/kitchen window though I have not taken them off. If I didn't have a $10 off coupon from Camping World, I may have ordered the string by itself from Dirty Blind Man--since that string is stronger. Seems that the plastic was all in OK shape, although I broke one of the ends taking it off. Maybe I'll send for replacements for that.