I don't get it either. There was no change to magic armor in Essentials, other than to call everything by its generic name (i.e. Feyweave and Starweave are both cloth armor). Your problem is still a glitch, and you should have an AC of 23.
I get it. Yeah. It's hardcoded now. Makes sense.
My question would be, are the odd masterwork armors still in the builder? For example, Stormscale. It's a +4 armor that has a +9 armor bonus (the standard bonus for that level now is +10), but it offers a +2 to Fortitude.