Actually, under Ikeda's formulation of the super-ko rule Black A is allowed because it is not a capturing move. Rule 4 in Part I states that, "If playing on a grid point places any stones of the other color in a removable state, the configuration resulting from removal of those stones must not be identical to a configuration that has already appeared in the game." Rule 4 may have been worded in this way to avoid awkward sentence structure in Japanese. Judging from Dia. 3-2-10 and the discussion in section 3.3, Ikeda intended the super-ko restriction to apply to all moves, not just capturing moves.

I never thought of applying superko to capturing moves only, but it does seem interesting, even if it's not what Ikeda meant. For one, it blends in nicely with the ko rule and makes illegal moves a bit easier to spot. I haven't seen this rule discussed anywhere, though.

This superko rule breaks eternal life, which normally becomes equivalent to a ko under superko rules.