Use a web browser to access the web interface for the printing system. Go to http://127.0.0.1:631/printers and find your printer. (You may need to add something in Terminal, it will tell you what)
Go to "Printers"
Find the printer with the problem and click on it
In the second drop-down menu "Administration" change it to "Set Default Options"
Go to "Finishing" and in the first drop down menu, select "Duplex" to "Off"
Scroll down and click "Set Default Options" then check the printer.
(Tested at LG on Major Fuckup using 10.9.3)