The fields on the MSI work in sort of a cascade from left to right.  The PO Ref is usually entered first, then as you tab out of the field it will look up the supplier connected to that PO.  If you don’t enter the PO Ref first (because there is no PO), but enter the next value, tabbing out of that field will attempt to look up connections.  This continues all the way down to the supplier as the last field in which a connection can be made - in the case there is no PO, no Project, no Advice, etc - no other connection but the supplier.

However if after you enter those fields and the supplier lookup action has been done to populate the supplier ID automatically, if you then go back and change any of those fields, the lookup doesn’t happen again to see that you’ve changed the supplier connection, my experience is that it happens only the first time.

When the user starts changing those fields after the supplier connection is made, IFS assumes you are doing something out of the ordinary and the scenarios become too complex to automatically update other things.  If the user is making a change, they should cancel the MSI and start again to make everything clean.

For example, you can match multiiple POs to the same MSI, but it becomes up to the user to ensure that all PO Ref’s numbers added to the MSI belong to the same supplier as the first one.  The user will eventually get the MSI locked where the matching can’t be done if the supplier or PO don’t match, but the error comes later and usually results in needing to cancel the invoice anyway.  We have this happen from time to time with a supplier that invoices monthly, but we receive upwards of 40 POs within the month.  The supplier wants paid once for all invoices and all POs matched to their invoice, so there is a lot of manual checking, if even one PO is entered wrong due to a typo, IFS doesn’t warn of this until the very end when there is an error in the matching, but PO Ref field can’t be changed at that point without cancelling and starting over.

Working with the MSI requires some care and precision to do things orderly, when you do things out of the order IFS is expecting AND it doesn’t tell you when you think it should, I would not consider it a bug.

Hi,
​​​@ShawnBerk explained, it is how the Manual Supplier Invoice window works - during invoice entry, before invoice is saved. But in your screenshot, we are in posting proposal - and here no changes happen automatically. Invoice is saved already. If you change PO number in this window, system is not  trying to change supplier (to the invoicing supplier of the PO) - instead it is trying to match invoice as it is with new PO. 
I think there’s an option in the company indicating what should happen, if supplier on the PO is different that on PO selected - match, raise error or ignore. Please check your company setup. 

@ShawnBerk 

@Adam Bereda 

Appreciate your input. will study and reply. Thank you.