This is for those of you that have only one spec with the Demonic Aegis talent:
Now before the patch, the armor would get updated if you changed talent spec.
Today in ICC, this was not a fact. I still retained the extra spellpower from the talent, even though I havent specced for it for destro.
So this is how it goes:
1. Use the Fel armor buff in a spec with the Demonic Aegis talent
2. Switch to the spec without the talent and ta-da!
An easy way to test this is by the message you receive when you try to buff yourself with Fel Armor:
"A more powerful spell is already active"
It will probably get hot fixed soon, so use it while you can!