Capital allowances : Balancing allowance

Hello sir, I have a problem in the concept of balancing allowance. What i know is that, we give balancing allowance when an asset is disposed off or the business ceases to trade. I was doing a question No. 255, where it states that, All the items in Special rate pool has been disposed off and short life asset 2 also sold. In the solution, there was balancing allowance on the remaining amount of short life asset 2 after disposal, but there was no balancing allowance on Special rate pool instead they charge WDA @6%. Is it a mistake or am I missing the law? Enlighten me. Thankyou in advance Harigovind Pandey