I have a 600ex-RT and when it is turned on and not connected to one of my Cameras, 6D and 70D, and it is in ETTL mode. When I attach it directly to the Cameras and press the shutter release button it goes into TTL mode and the flash is fired at full power. I go into the C.Fn settings , #5 is already set at 0: (For ETTL) but I select it again and then the flash reads ETTL but as soon as I fire it again it goes back to TTL . What is a possible cause for this problem? Thank you Kindly