No, I didn't have it in slave mode. I was photographing indoors in TTL mode and after a few shots I noticed that my red Pilot light started flashing. Since I had never saw this happen before, I turned the flash off and then back on. Everything worked fine for a while, but then it happened again. I didn't change any settings on my flash. I am concerned that it might be malfunctioning and couldn't find any info online.