Solution : https://service.sap.com/sap/support/notes/394317 (SAP Service marketplace login required)
Key words : 
function module cx_sched_via_operating_time, attached program corrections, scheduling margin key, adjust basic dates, basic dates, program error, operation dates, basic date, basic finish, planned order
Related Notes : 
       
| 632951 | Basic date in planned order incorrectly adjusted | 
| 328307 | Start/finish date is on work finish/start |