This is resolved in versions 2.9 and above. To resolve, please, update to one of these versions.
Alternative resolution: 1. Open the pledge for edit 2. Change the designation for the pledge and the payments when prompted 3. Save the Pledge 4. Open the pledge again for edit 5. Change the amount of the pledge as you would normally along with the designation 6. Update the installments 7. Add the adjustment information 8. Save