It's definitely bugged, I've seen other people complaining too. I crafted it last week unaware of this until it happened to me and I lost a game because of it.
Sometimes it does let you exile your permanents and sometimes not, it's inconsistent. I think it's been bugged for months now, so it's probably not an easy fix.
It's more that we hadn't been aware of the issue. We're working on a fix this week, not sure when it'd go live though (very likely M21-release at the latest though). #wotc_staff