Casual Payroll - Overtime hours being deducted from base hours

We have a handful of casual staff members, however we have an issue in payroll for only one of our staff members when processing their pay.

When entering base hourly, then entering casual loading both process fine, but when we enter their overtime hours the hours then deduct themselves from the base hourly. We can not figure out why this is happening or what we need to change to rectify the issue

eg

38 Base hourly

38 casual loading

12 hours overtime

it then changes the payroll to

26 Base hourly

38 casual loading

12 hours overtime

Has anyone had this same issue and if so, how did you fix it?

Thanks in advance for any guidance