Although the bug has to do with his fireball, the most practical setup is from this super, so I'll put this here. There is a certain point in his fireball's hitbox where it cannot be blocked if it covers the opponent's sprite in a specific place as they are getting up. Two characters, Kensou and Brian, fall victim to this bug in such a way that simply buffering an A strength fireball immediately as the super is ending will be unblockable as it reaches them. You must not perform any move before the fireball hits, or they will be able to block. On Brian you can actually combo a second C Maiden Masher if you just wait until the fireball hits (Kensou requires some very specific distancing from the corner).

Kensou and Brian are the ones listed at 46, which is the number of frames it takes for them to get up. This creates the perfect timing for the fireball unblockable for you. Any character with a smaller number cannot be hit with it. All characters with a larger number can be hit, but you must manually delay the fireball the appropriate number of frames (and it is a single-frame window of timing). So for example, at 47 frames is Terry and Saisyu. You must delay the fireball exactly one frame after you've recovered from the super to make the fireball unblockable.