I've talked to Microsoft several times about their 'linescroll', it jsut doesn't do a lot of the things that you think it might because they do a bunch of things in the form that are not exposed.
If I understand correctly, the user has the SOP Transaction window OPEN, and you want to scan and insert new lines into a SOP Order?
I usualy try to do that with the form closed - use eConnect to send the lines to Dynamics and they open the form when you're done.
However, the effect that you're describing might be caused by an unbalanced order. When you add the line, the total is not correct any more. Or the subtotal, etc. You'll have to retotal the SOP10100 if you're not using econnect.
This is the rub. If the form is open, you insert a line, and you need to retotal the order. You retotal the table, but that doesn't change the form. Big, hairy mess.
Better to do it with the form closed.