External HDD Dock Pushing power back to mainboard


I purchased a CnM Lifestyle Sata to USB hdd dock. All seemed well with it until one day I powered down my PC but left the dock plugged in to the USB port.

I noticed that the HDD and power light on my Computer remained on.
removing the cable from the computer turned the lights off.

A check with a Multimeter showed the cable carrying 5v even when not connected to a PC, so it was sending this back to the PC when it was unpowered.

Is this likely to harm my mainboard?



I’d return the unit and get another, similar product. Seems as if the manufacturer of that unit failed to add some diodes in order to save two cents.
Such might cause damage to the motherboard in worst case.