Generally when plugging two ESCs into a receiver that both have BECs, I just remove the +ve wire from one of the connectors and tape it up out of harm's way. As the specs state, they should only be supplying 5V down the wires to the receiver so if you're getting 16.8V at it, there may be a problem with the ESC, but that sort of fault isn't a common occurrence as far as I'm aware. Have you got/are you able to get a picture of the way you've got it all connected, just to see if we can spot anything untoward?