Mentioned it before, just putting it here finally.
After invoice created... first invoice sending partial number of items...
shows Buyer pays 0 (taxes) and seller pays 0
however, after that, the next partial send, it shows buyer pays 0, and sell pays ($$), it also doesnt change if you lower the amount of units. I know its a bug, im just wanting clarification if its a Graphical bug, or its actually gettting charged?
(yes, its the same country, literally accross the street!) lol
Thanks! 
What business type are you seeing this?
And it is a display issue. Thank you for posting this.
Production.
I am sending it via a tranport to someone in the same country. (across the street)
it happens in a specific manner, i have found.
if its phones/cars/drones. whatever the max send is... (total invoice)
if you send it all, it shows 0 seller fee’s.
if you send 20 out of 40(total invoice) the FIRST time, it shows 0
however the next time you send ANY number, it says the total for this shipment paid by the seller is $$$
Wether you send 20, or 10, or 5… still says the same $$$.
hope that helps.