XP-G NW tint shift question

My Eagletac D25c clicky with NW XP-G R4 is suffering from (dramatic) tint shift at the 5 lumen level. All the levels are current controlled. Moonlight: excellent. 5 lumens: violet. 50 lumens: excellent. Turbo: excellent etc. My quark AA has the same NW XP-G (4B tint) and is also current controlled on all levels; however on the comparable 4 lumen output, there is no tint shift. Other than the 5 lumen level, the tints are nearly identical. Is there a difference in the circuits used that may affect the tint? (Neither one uses PWM).

I might add that I am used to the usual XP-G/XM-L tint shift at lower drive currents, usually adding a little greenish/yellow tint in my NW versions. (which I dont really care about). This one is different; it goes from neutral/yellow-greenish to violet back to neutral.