performance problem Lightcache the 2nd

[QuakeMarine1]

sorry to stress again but I have a reproduce able issue

I run
Asus Z8NA D6
4x4 gb KVR1066D3Q8R7S
2x E5520 (2*4 + HT)
XP 64 SP2
max201064 SP1
Vray SP3a

I run a scene with LC and threads set to
8 = 50% CPU usage - correct
4 = 25% CPU usage - correct
2 and 1 threads = correct
but
treads 16 = 50%-60% CPU usage
now I DISable "show calc. phase" for LC
= 100% CPU

I ENable "show calc. phase" + use Vray frame buffer
= 100% CPU usage

what is the matter to use 3dsmax2010 + 3ds frame buffer + show calc. phase + 16theads for LC

simple teapot scene in 800x600 pix
no texture
renderers.current.system_numthreads=0
vray ram settigns default
render and IRR render = 100%
max2009 - all 100%