Plenty of people in this thread are experiencing it my way, so I doubt it. And if it is a bug, then I'm glad I have it, since its making it work like it should.
Regardless, look at the post just below yours. The argument is Alteration vs Illusion in regards to the invisibility mechanics in Skyrim, and to be honest, the post below yours explains it pretty well.
"Nope, it bends light. Don't believe me? Then go look at the lore and read the books on Illusion and its right there. 3 games and its official lore? You just made that up, lol. "
Are you freaking kidding me?
"Illusion is one of the five schools of magic in Skyrim. Illusion magic focuses on changing the perception of the world from the viewpoint of the target. Increasing this skill reduces mana cost when casting illusion spells. Historical information about the School of Illusion is provided in the lore article.
In-game Description: The School of Illusion involves manipulating the mind of the enemy. This skill makes it easier to cast spells like Fear, Charm, and Invisibility."
- http://www.uesp.net/wiki/Skyrim:Illusion
"Illusion affects the perception and mind of living subjects."
Spell effects of the College of Illusion alter the perceptions and thoughts of living beings. Illusion effects blind, illuminate, paralyze, and silence, calm or enrage, charm, distract and camouflage, and render invisible."
- http://www.uesp.net/wiki/morrowind:Illusion
Use the school of illusion to create light, conceal, charm, paralyze or alter an actor's aggression or confidence.
- http://www.uesp.net/wiki/oblivion:Illusion
The only descrepency is in Oblivion, and it still acts on the AGRESSOR.