We will not inactivate a deduction, but we will not take it based on the end date and how it falls with the pay period dates, so yes it would not be taken in the payroll, but it would typically stay active. The only time I see the auto inactive happen is with Class ID changes if they are doing that, and the class does not have the benefit or the deduction then it will inactivate it.
You could always install the detail activity tracking tool, it is free, then it tracks who is changing the record and when if this will help you narrow it down.
mbs.microsoft.com/.../NOAM_PSTL
Thanks
Terry Heley
Microsoft