When acis_process_events is used to reprocess event data, it does not unset status bits in the input data file. For example, acis_process_events does not recalculate the bad pixel status bits. If events have status bits set in the input event file, then the values are always copied to the same bits in the column STATUS of the output file. If the badpixfile is set to a value other than "NONE" (the default), then only additional status bits can be set in the output file. This limitation will be fixed in a future release.
The exception to this is the VFAINT background cleaning (status bit 23). As of CIAO 4.0, previously set VFAINT status bits are unset before the check is done again.