Copied assignments are automatically giving students 0s

[dewittel]

I have occasionally copied assignments from old Archived Courses and never had this happen.  This year when I copy the assignments and change the due dates (before publishing with updated due dates). It automatically gives every student a 0, I have deleted the old dates and saved before publishing the assignment.  Doesn't matter.  But having to copy and paste the assignments or go back and delete all the 0s is time consuming and frustrating. I also have to have at least 1 grade inputted on Canvas before it will sync the assignment to PowerSchool. 

Has anyone had issues with this? 

[DrNufer]

Just curious, you delete the old dates and save, but do you first set up a new due date for the current term before saving?