This is what mine is doing (as tested with the standard body PLUS the CR123 and single AA adapter tubes):
1. Batteries that came with it work fine. All rechargeables work fine.
2. Single Tenergy CR123A primary (3.1 volts brand new), flashes bright and then immediately goes to dim
3. Single Lithium, Energizer AA primary (1.81 volts new), flashes bright and then immediately goes to dim
4. Two Lithium, Energizer AA primary (3.62 volts), flashes bright and then immediately goes to dim
Software low voltage is 0.9 volts for one cell and 1.8 volts for two cells. This explains why one Li AA doesn't work. A new Li AA measures 1.8 volts, so the light thinks it has two AA cells in it that have dropped below the 1.8 volt threshold.
But why don't the CR123A and 2xAAs work? One CR123A is 3.1 volts, which is above the 1.8 cutoff. 2 AAs is 3.62 volts, also well above the 1.8 volt cutoff. My guess is that the high cutoff is right at 3 volts. I did review the website specs and it does say voltage range 0.9 - 3.0 volts, which covers rechargeables and alkalines. But the three replies I received from tech support only mentioned low voltage cutoff, so I am only guessing. I also have no idea what the single cell voltage range is, since 0.9 is low, but 1.8 is low cutoff for two cells. Must be something like 0.9 - 1.5 volts, since the light is rated for Alkalines.
I guess it boils down to user error. Light isn't designed to work with Li primaries.
Interestingly, all the other modes except high work just fine with Li primaries.