Comment 40 for bug 885118

I just went through the same problem while installing Ubuntu 12.04 Unity. My printer is a Brother 2270DW, but it has been working perfeclty (duplex printing) using the 2170W driver under Linux Mint 11, 12, and 13. Selecting 2 sided printing in job options was possible, but the setting would revert to one sided when the apply or approve button was clicked. Under Mint 13 I had the same problem initially, but after logging out then logging back in, the 2 sided printer setting worked. This was not the case in Ubutu 12.04.

This is the printer setting that was selected by defalut:
Brother HL-2170W Foomatic/hpijs-pcl5e (recommended)

I found Peter's comment (#3 from 2011-11-18) about using the CUPS web interface (http://localhost:631/), and this solved my problem. It was under the "Modify Printer" section, which required inputting the Administrator password. This allowed changing the setting to 2 sided printing. Upon going back to the Printing Properties, that change was made!

Note: this setting is hidden under a "+More" button, which is just under the Pages per Side box.