when Kensei took a swing with his normal heavy attack i hit him first by normal, fast attack and this wasn't brake/stop his animation/attack he hit me with his first swing.. is this a features or bug?
The Kensei's third hits in any combo (combos counting GB's, not just weapon swings) has special effects. From the top it's unblockable, from the sides it cannot be interrupted. This side-attack after a 2-hit combo of basically any sort of mix-up is probably what you were talking about.
