Overview:
The Order Total Quantity value in the Order header differs from that of the Order lines.
Root Cause:
The Order header calculates again if the user deletes the order line through the order VisualForce page. If the Order line is deleted or modified, the quantity on the Order header does not change.
Solution:
If the user clicks on Edit and then Saves the Order without changing it, the Order Total Quantity is recalculated automatically.
Related Documentation:
N/A