That's why I said that might be something that was overlooked, as it's the only case. In other cases when he bent, he did glow (including when he bent to give korra energy bending/ unblock her bending).
http://25.media.tumblr.com/tumblr_m6...kmgho2_500.jpg
http://24.media.tumblr.com/tumblr_m6...mftno1_500.jpg
http://images.wikia.com/avatar/image...ion_Turtle.png
In all cases of energy bending you can clearly see that the eyes glow and the person being bent ALSO glows, though not at the eyes. It's on the hands of the one doing it.
That's what makes the first picture an anomaly - he's energy bending, yet the hands/ eyes are unaffected.
The glow for aang/ ozai is strange, and possibly due only to the massive conflict. It doesn't fit with what we know of energy bending, but characters within reference it so it had to have taken place, at least partially, where everyone could see it.