Disposal of a revalued asset

Dear Sir, In the BPP text book, on disposal of a revalued asset, they credit disposal account with the balance on Revaluation surplus account. Therefore, the credit balance on Revaluation surplus account is realised in Profit on sale account. However, in one answer from the revision kit (8.20) for the same issue, the calculation of profit on disposal of non-current asset is nothing involved with the Revaluation surplus account. Accordingly, the balance on Revaluation surplus is transferred to retained profits reserve, but not be reported as profit in the statement of profit or loss Can you please help explain this? Thank you!