I have not seen this, but I'm wondering if SY0CTL.SOA might have corrupted records? I've experienced other issues when making changes to legacy modules in setup options and they stick for a while and then at some point the are set back. If I remember correctly there is a record ins SY0CTL.SOA that should mirror the settings in WO0xxx (work order options file) and the SY0 record may write back over the WO0 record.