Shield wire in Micro USB extension lead appears to be ground
In that case your cable is most likely defective. I have seen products where the shielding wires are Ground but then there was no black wire. 
I tested myself on my USB from Samsung and I get 5V between Red and Black and 0V between the shielding.

Having Shield as Ground has the risk that if something shorts to the Shield due to any defect that it is shortened to  Ground.