Minimal failing case:
(s/def ::key-spec (s/or :kw keyword? :str string?))
(s/def ::map-spec (s/map-of ::key-spec identity))
(println (s/unform ::map-spec (s/conform ::map-spec {:a :b})))
java.lang.UnsupportedOperationException: nth not supported on this type: Keyword
If keys are not conformed, we should also not attempt to unform them.