In review https://reviews.apache.org/r/37032/ there was some debate about how to handle "fallback" of setting/getting Unix permissions on Windows. That is, on Windows there is not native support for "group" or "other" permissions, so when a user gets/sets group permissions, we can either (1) make that operation a no-op, or (2) "fall back" to getting/setting "user" permissions.
Originally the review opted for a "strictness" flag, so that at compile time users could pass in a flag and change the "fallback" behavior to be "strict" instead, ignoring group and other permissions setting.
Currently (Sept 10 2015) we have pulled this option out, and only allow "strict" permissions. This will probably break stuff later, but we can reevaluate later.