I have found that invoices are being silently altered when I hit 'Post', using ledgersmb 1.3.22. When a line's part number is edited, this change is lost.
Steps to replicate:
Go to Sales->Sales Invoice to enter a new invoice.
Enter a part number for Item 1
Note that the price, description and other details for line 1 are filled in
Change the part number for Item 1
Note that the new part number is correctly retained
Note that the part number has now reverted to its initial value - the change has been lost.