This is how the pension postponement system works, if the age or earnings criteria aren't met at the end of postponement then the worker will be postponed again for a further three months.
The worker can, however, opt-in at this point.
You can view postponement details for a worker in the following menu:
Go to Workers and then go to Payroll Details.
Select Worker Pension Postponement and enter the Worker Reference.
Press TAB.