infotype 15 = additional payments

Dear All

We have added value in infotype 15 = additional payment and subwage type 1054 = commission of Rs 5000 ( it is one time payment ) when we check the payroll system is calculating Rs 5000 * 12 ( month ) and adding the amount in gross salary i..e Commission is one time payment but system considering 12 month payment .

Also we are making payment against credit balance from tour in the infotype 15 , for that also system is considering for 12 month payment and adding in to gross salary

Please suggest the same