What do you mean double set?
You’ve plugged two riser cables into each other like an extension cord?
I did that once and the PCIe slot caught fire after 10 seconds… I screwed a $300 mobo, I was so upset…
I dont use the prefab power cables. The power allways goes straight from the connector to the card with no “feedback wire”!
So i have never had any worries with this issue, and i have connected two extenders after one and another. one active and one passive.
If you connect two active cables i can see that this might be an problem, especially if you connect both the power plugs :P