When the valves in the SUPERFICIAL veins stop working, a similar problem occurs but in the superficial system. 

So during movement, the blood is pumped up both deep and superficial veins during muscles contraction - ie: PUMPING the leg.

When the leg RELAXES, the pumping stops and the blood starts to flow down both deep and superficial vein systems.

The working valves in the deep system stop any back flow down the deep veins but the valves in the SUPERFICIAL veins are not working.

So in this situation, blood flows back down the superficial veins that have lost their valves. As you can see this is a very similar end result to the valves not working in the deep system.

However, this is the very part of vein surgery where the misunderstanding has occurred over the last 100 years that has meant that leg ulcers, skin changes at the ankle and varicose veins have been treated so badly.