Are you firing the YS-D2 with a fiber optic cable from the camera? How is it attached? It it possible there is light entering the cable at the camera end?I'm curious about your setup Skeptic 14 and was hoping you could share your experience with the YS-D2. On my TG4 rig I recently replaced a single YS-03 with a single YS-D2. Have noticed in pool testing and one trip that the YS-D2 sometime seems to randomly fire after taking a shot in TTL mode. The TG4 internal flash is not firing and it is not recording an image from these "random" flashes. I estimate that they are not full power flashes as I can look at it without being blinded. I cannot find anything in the Sea & Sea manual that explains the behavior and was hoping someone with more experience could shed light on this.