The current (and past) Stylize/Glow effect shows some unlogical behavior:

1 It lets glow dark colors (under the treshold) too.
Even when the Glow Operation is set to 'Add' and Glow Is Based on Color Channels (Default), a dark shadow like halo appears around the borders of a layer.

2 Another strange thing: When Glow Intensity is set to 0 (zero), the black glow still appears.