UnitCastingInfo 9th parameter, notInterruptible, is always returning false

[Terenna]

Good morning,

I've performed a search on our forums as well as google for both UnitCastingInfo and interrupt. I see no documentation

here: http://wowprogramming.com/docs/api/UnitCastingInfo,
here: http://wowwiki.wikia.com/wiki/API_UnitCastingInfo, or
here: http://wow.gamepedia.com/API_UnitCastingInfo

that the API has changed. As such, any cast, be it an interruptible one or non-interruptible cast such as mounting or hearthing, is always returning false (aka interruptible).

Am I missing something? I haven't seen anyone post about this so I feel like I'm taking crazy pills.