Surefire LX2 flickering on low (using 14670 type cells)

My recently purchased LX2 exhibits the following behaviour:

On primaries both levels work just fine. Using AW's old 14670 rechargeables (which I've been using in my old L2 without problems) I can see that the high level is lower than on primaries but that was expected. What worries me a bit is that the light is flickering on low.
(To provide a bit more detail: If the light is switched from off or from the high level to low it comes on at a certain brightness only to quickly start fading to a lower level and starting the mentioned flickering.)

Is the flickering normal? Will it happen after running down a set of primaries as well? Does using 2x RCR123 (3V / 3.7V) help avoiding the problem? What is causing this behaviour? I would've expected to see problems on "high" shouldn't the battery be able to power the light properly...

Thanks a lot for you help,
Undark

I'm guessing that the LX2 is not designed for Li ion rechargeable, since I hardy ever heard of surefires running on Li ion cells (except modded ones).

I would use primaries until someone can confirm that you can safely run 14670 (never heard of this format:S)

I see that Surefire is selling 16340 LiFePo rechargeables, so I'm guessing that they should work, but confirm it with someone who has experience with it before you start using in your LX2. (maybe contact Surefire)