My light also flickers while screwing on the end cap, but never once it's screwed down all the way. Although I have no proof, I think it's related to how the light cycles through the different brightnesses. The light changes mode in response to moving the switch to "on", then slightly off, then "on" again, rather than a mechanical switch with several different indents for different light levels. This makes me think the light levels are controlled by a circuit, and maybe screwing on the battery cap sends confusing on/off signals. Or maybe notMy light doesn’t have the small glow in the LEDs when in the OFF position as noted by Jim in post #42, but it flickers as I turn the end cap. My gut feel is that we both have faulty ON-OFF switches, but the light itself works fine otherwise, so I’ll live with the flickers.
-Don