Its not faulty, each and every GPU core gets tested for what it will become, some have hardware failures and become a 980Ti instead of a Titan, or a 390 instead of a 390X, sometimes that failure is the core volt leakage, and to understand what and why this is and happens you have to understand how a die is manufactured.
Core voltage isn't just applied at one magic spot to the silicon, instead it gets pushed through multiple traces so the voltage is stable to ALL the circuits on the chip, why you ask? Due to the size of the manufacturing process the traces (copper wires) in the die are TINY, and each may only be capable of carrying a tenth of the amperage at the rated voltage.
Next we have to understand that silicon is unlike copper in that it becomes MORE conductive as it heats up, this compounds the problem as once over "the bend of the knee" where voltage input correlates closely to achievable frequency, but at the bend the effect becomes exponentially less efficient and voltage is lost through heat, which in turn causes more leakage, and in turn more heat, and the voltage drops, the voltage controller without any limit would kill any chip.
So W1zz probably has a very bottom of the barrel sample, luck of the draw, that needs more voltage at rated speeds, which correlates directly to Watts of use, and higher heat output, overclocking makes the problem worse as it creates more heat, and requires more voltage...which.... well you should get the picture.