Leave Accrual

Hi. I am new to MYOB & payroll and am chasing assistance with regards to the following... I have an employee who has purchased leave in lieu of a pay increase.  I have both the wages and entitlement categories set up and if I enter hours in the purchased leave section when processing payroll it will deduct from that entitlement and his normal hours will accrue in all three entitlement categories correctly. However, when he takes personal/sick leave or uses his normal annual leave it won't accrue any hours to this entitlement category like it does to sick leave and AL.
I hope that makes sense!