I just got a (used but Excellent condition) Canon BG-E13 Grip for my EOS 6D. I immediately discovered that I have to put in/change batteries with the grip OFF the camera, then mount the grip on the camera. Removing/replacing battery holder with the grip ON the camera results in the camera not powering-up. This is happening with different battery holders, for LP-E6 and AA batteries. The same holders are not a problem on my EOS 60D (yes, the battery holders are the same with a BG-E13 and a BG-E9). This can't be normal, can it?