Now that I think about it, I don't think Simba and Riku have invincibility frames, either, for Healing Herb and Cure Potion, respectively, but their animations are faster than Auron's (I think I saw Riku get interrupted in that last project video of mine).
That theory you provided for Auron may hold true for them as well. However, they really should have made it so Auron's MP doesn't drain if Healing Water doesn't take effect. The same applies to Simba and Riku, but again, they're faster, so when they're interrupted, which I've only noticed once on Riku (see above), the healing has already taken effect.
Comments on Profile Post by Amaury