Payroll Vacation Accrual Error (8.03.305)

We are running 8.03.305k and I am trying to solve a payroll problem
that has apparently occured for a long time over several versions.

We accrue vacation hours with each payroll and run payroll every 2
weeks. Occassionally we will have an employee whose accrual is
wrong. The person who used to run our payroll kept a manual log and
made the necessary adjustments and never thought to ask for help with
the problem.

On the current payroll we have an employee who had 230.5 hours of
available vacation on his last check according to the manual log and
the payroll person says it matched his check or she would have
adjusted it. When I look in his payroll record it shows that he has
234 hours and accrues 6.5 hours per payroll. The current payroll has
not been posted and it shows 240.5 hours on his check.

Has anyone else run into problems with this or have an idea where to
start looking? It seems strange to me that it would be an user error
since it should be an automatic process.