Question regarding Frontal Stun Immunity

[Killval]

In regards to the Ogre racial of Frontal Stun Immunity or FSI, my question is this. So say you are casting a spell with your back against the wall, channeling skill is maxed whatever, so none of that can be an interference with my question. What happens when you are casting as an Ogre and mid-cast a mob connects with a bash, I recognize you DO NOT take the stun effect, however, will the Ogre be interrupted of his spell cast regardless? Because if you do get interrupted, but just do not take the stun effect, then I'd say the usefulness of FSI is heavily mitigated by that fact, and regen would trump it, IMO. However, if you can actually continue to channel your cast through a mobs connected bash without receiving some sort of interrupt(outside of channeling skill & push), then I think it should be as heavily lauded as it is. I've never been able to find a distinct sure fire answer to this question. Any perspective on this from max level Ogre Shaman who can indeed confirm this would be greatly appreciated. Thanks = D (Please don't turn this into a BiS race pick for Shaman lol, that's been done to death, I'm just interested in a mechanics question regarding the FSI racial)