Box 1 and Box 16 on W2 not matching

Last year we have a handful of employees in which Box 1 (fed wages) and box 16 (state wages) did not match on the W2. The difference was always the same amount as a benefits adjustment. Usually the employee terminated and benefits were not turn off in time and we deducted, then needed to reimburse the employee.  Box 16 is always short the reimbursement amount, and box 1 includes it.  Any ideas?  I'm trying to get to the bottom of it before we get to year end.