On the T5008, if your Box 21 is greater than your Box 20, then you have a gain. Generally, it is expected that your taxes would increase according to this gain.
However, your overall taxes owing is dependant on your overall tax situation. If your gain is small, and overall your income level is low, it is possible that you have sufficient other credits/deductions to offset your income and your final tax amount is unaffected.
On the T5008, if your Box 21 is greater than your Box 20, then you have a gain. Generally, it is expected that your taxes would increase according to this gain.
However, your overall taxes owing is dependant on your overall tax situation. If your gain is small, and overall your income level is low, it is possible that you have sufficient other credits/deductions to offset your income and your final tax amount is unaffected.