I don't have MegaPOV to compare with and I can't remember anything about glows,
but I'm wondering if this might be incorrect behavior.

Hollow doesn't seem to matter if the glow is used in a light, and maybe that's
instended, however a standalone glow will only disappear if viewed from within a
non-hollow sphere (I have not checked other objects). In other words, if viewed
from outside a non-hollow sphere the glow still shows as though it fills the
sphere.

And not only that, another glow outside the sphere will disappear when it's on
the other side of camera if that semi-transparent sphere is non-hollow.

Scene file to test with, because I know that probably sounds confusing.

/* test glows using hollow and non-hollow sphere (Envelope) */

#version 3.7;

global_settings
 {
  assumed_gamma 1
 }

#local Envelope=no; // enclose non-hollow sphere around camera
#local Hollow=yes; // make hollow?

camera
{
 location <1,3,33>
 look_at <0,0,0>
}

light_source
{
 z*3, <1,1,0>
glow {
  type 0//0 | 1 | 2 | 3
  location <0,11,-11>
  size 0.5
  radius 4
  fade_power 2
 // color <1,0,0>
  //rotate translate
}
translate <-10,-10,-10>
 rotate <15,-45,0>
}

glow {
  type 3//0 | 1 | 2 | 3
  location 0
  size 11
  radius 33
  fade_power 2
  color <1,0,1>
  //rotate translate
}

#if (Envelope=yes)
sphere{0,36 hollow off pigment {rgb <1,0,0> transmit 0.5}}
#elseif (Hollow)
sphere{0,33 hollow on pigment {rgb <1,0,0> transmit 0.5}}
#else
sphere{0,33 hollow off pigment {rgb <1,0,0> transmit 0.5}}
#end

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