Treatment of Social Security seems to be wrong

I just got reassessed by RevCan. I receive US Social Security ( lets say $2000/ year) no US taxes withheld. In the section Additional Deductions  two amounts are shown:  the $2000 in Other Income and Deductions and $300 in 15% exempt portion of above making a total of $2300. According to RevCan only the 15% portion is allowed and in reviewing the tax rules I agree. Consequently I received a reassessment of close to $300. I am not complaining just suggest you fix it for 2024.