I had a light that did the same thing. I turned it in for warranty work but when I got it back it still did it. It seems do it at exactly the same rotary position.
I have a Rotary that did the same thing. I sent it in but it still did it when I got it back. It was one of the later models with the noisy contacts. It seemed to do it in almost exactly the the same dial position.
I have a Rotary(several years old) that random turns on by itself. Happens several times per week. When it turns on I can't turn it off but have open the battery compartment to reset the light. I guess the light needs to be sent in.
+1. I had a gritty one that had sporadic problems with the switch. Sent it in for service, came back with an even more gritty rotary but at least the switch is fine.