Vapor retarder placement – GreenBuildingAdvisor

I Work for a small builder, we use a lot of 1 inch XPS on 2×4 walls. CLZ5A In one of our homes we have some dead space on exterior walls. The inspector made us put foil faced kraft paper to encapsulate the unfaced fiberglass batts. This raised some red flags in my mind. The wall outside to inside is

hardie

1 inch xps

osb

2×4 with unfaced batt

foil faced kraft paper

deadspace

gyp board

The osb and framing is stuck in a class 1 vapor barrier sandwich. 

When I raised concerns over this the question was brought up about showers. We use Kerdi membrane which is class 2 VB but the tile and epoxy grout are all but vapor closed. But showers of this sort are code approved in assemblies with 1 inch XPs. I can’t wrap my mind around how one is allowed and one is dangerous. Can someone explain?