Ifrs 2 (deferred tax consideration on sars)

According to ifrs 2, an entity recogizes expense for the share based payments over the vesting period but the tax authorities dont recognize the expense over that period because the shares have not yet been exercised. Correct? Then why do we take the carrying value of expense in accounting books as 0 and take the amount of expense in tax books? Shouldn’t it be the other way around? Because if tax authorities dont recognize the expense, then shouldn’t their value be 0?