PAYROLL - pay basis keeps changing each payun

Every time I do a pay run, the pay basis change from Salary to Hourly. 

I have to manually change this every pay run. Is there a way to change it, and it's final? Why is MYOB keep changing the pay basis? 

Is it because the timesheets are imported from Tanda, or some pay items selected are hourly and salary? 

Veronica