jemiris wrote:1. From where the due date comes from 
See my previous post were I explain that. The tricky part is which calendar is selected.
If the user doesn't have a set calendar, then the calendar of the task is used. If the task doesn't have a set calendar, then the calendar of the process is used. If the process doesn't have a set process, then the default calendar is used. For this reason, set a calendar for the user and see if that fixes it.
I have no idea what might have caused the bad calculation of the due date. Maybe you have a bad time in APP_CACHE_VIEW.DEL_INIT_DATE or maybe the calendar is bad or maybe you have a strange value for the expected time to complete in your task properties.