I've lately noticed some really odd behavior in 3.7 ("odd" as compared to 3.62.)
Max_trace_level seems to be completely OFF or ON now, when its value is changed
between 1 and 2 (or anything higher than 2.) In other words, a value of 2
produces the same visual result as setting it to its maximum value, or so it
seems. The other odd thing is that the render statistics always return a 'Max
Level' of only 1, regardless of the max_trace_level setting or the number of
semi-transparent overlapping objects in a scene.

(This is in Windows XP, on a single_core AMD machine, using 32-bit v3.7 sse2.)

Here's a small test scene, with a switch for rendering in 3.62 vs. 3.7. Just
semi-transparent nested spheres.
----

// The switch...
#declare version_to_use = 2; // 1 for v3.62, 2 for v3.7

#if(version_to_use = 1)
global_settings{max_trace_level 5 assumed_gamma 2.2}

background {rgb .7}

#declare C=1;
#while(C<=40)
sphere{0,1
 scale .1 + .20*C
 pigment{rgbt <.1,1,.1,.99>}
 }
#declare C=C+1;
#end
#else
#end

#if(version_to_use = 2)
#version 3.7;
global_settings{max_trace_level 2 assumed_gamma srgb}

background {srgb .7}

#declare C=1;
#while(C<=40)
sphere{0,1
 scale .1 + .20*C
 pigment{srgbt <.1,1,.1,.99>}
 }
#declare C=C+1;
#end
#else
#end

// for both versions...
camera {
  perspective
  location  <1, 1, -25>
  look_at   <0, 0,  0>
  right     x*image_width/image_height
  angle 67
}

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