How strict is Skyrim's 'Mage Armor' perk on the armor restriction?

So I'm looking here at the Mage Armor perk, and it supposedly doubles Stoneflesh's effectiveness if 'not wearing armor.'

I just picked up a mask called 'Morokei' that increases Magika regen 100%. Only problem, it's classified as light armor.

Will this destroy the effects of Mage Armor?

You will no longer get the benefits of mage armor if you wear any kind of armor.

The only exception to this rule is shields. Wielding a shield does not negate the effects. You receive the benefit of this perk along with the usual benefits of a shield.

Yes, all masks destroy this perk effect as long as they are in use because all of them are considered as armor. To get the bonus of Mage Armor you can only use items that are considered as clothes. However, shields are an exception (you can use a shield and have the bonus of Mage Armor).

1) Morokei is a Daedra artifact/Dragon mask and all Dragon masks fall under the "circlet" category. This means that they will in fact work Mage armor, and, it should be equip-able with the archmage robes for what its worth as well. Haven't tested myself though. Also, if it wasn't clear, you can use the heavy armor dragon mask as well I think. (source - http://www.uesp.net/wiki/Skyrim:Alteration)

2) Mage Armor works with any circlet and shield (mentioned in other comments - just confirming it works)

3) Nothing "destroys" the effect of mage armor from my understanding. If you have no cloths, cast mage armor, and then equip heavy armor, the full armor bonus + heavy armor will be applied. However, if you re-cast while its on, then the buff will go away.