Mmm, mine's a bit temperamental too, it likes to flash red codes even when fully charged. It does seem to settle down after a few on-off cycles though.
There doesn't appear to be a user manual for the Lighter-S, but the Lighter manual suggests that holding the power button for 3 seconds while turning on toggles the auto-shutdown mode on and off. While off, it should flash green twice a second rather than once.
Not that it should shut down while being used though. Have you spotted it flashing red at all?