Switch to the Evo View, that will let you use multi screens.  The reason the Classic View Lines screen it like that is because it is loading a modal form (that locks the rest of Evo) when I was not doing it that way we were getting AV errors when returning from the lines screen.  
 
Use Settings,US-A and change SO-A to Evo View.

I've been using the Evo layout and think I can get used to it, but there is one annoyance. Since I switched to this view, every time I create a new PO and print it when done, once the printing is complete I get a "Vendor ID cannot be blank" message...