Reason why Invoice is Unlinked from the Sales Order

Behavior of Invoice and Sales Order status:

 

When Invoice's item is changed, Sales Order > Related Records > Invoice linked is disconnected

When Sales Order's Item is changed, Sales Order > Related Records > Invoice linked is still connected

Either of the above, Sales Order > Status will change to = From Billed to Pending Fulfillment

The above changes apply to these two different scenarios:

 A.    Sales Order's Item is Edited

-       An invoice is created through Sales Order > Bill button

-       Sales Order status is Billed

-       Edit Sales Order's Item

Results:

Sales Order's status is Pending Fulfillment

Sales Order > Related Records Tab > Invoice is still linked

 

 B.    Invoice Line Item is Changed

-       An invoice is created through Sales Order > Bill button

-       Sales Order status is Billed

-       Change the Item on the Invoice and Save

Results:

     Sales Order status is Pending Fulfillment

Sales Order > Related Records Tab > Invoice is NOT connected to Sales Order anymore

System Notes documents the Billed value and goes back to Pending Fulfillment. The same behavior when Deleting an Invoice linked to the Sales Order