It's true...In my ST-Link (Purple colour), Pins for GND are 3 and 4.However, all's ST-Link V2 Photos that i can see in internet, pins for GND are 5 and 6.
Red arrow shows ST-Link Programmer for SWD mode. DFU mode needs Micro USB wire and enter in DFU mode. I will do it again in SWD checking all wires. Do you want to tell me that mi ST-Link programmer has the wires position changed?GND in my ST-Link is ...