I can confirm that this bug still exists in Ubuntu 16.04.5: specifically, I tried printing two pages of a PostScript file from Evince with Duplex set to "Long Edge (Standard)", and instead of a single sheet with both pages, the printer printed on two sheets.
I also had the following error on the terminal from which I launched Evince: "fatal internal error -100" eight times, without a newline between the repetitions.
It would be good to find a solution to this problem.
I can confirm that this bug still exists in Ubuntu 16.04.5: specifically, I tried printing two pages of a PostScript file from Evince with Duplex set to "Long Edge (Standard)", and instead of a single sheet with both pages, the printer printed on two sheets.
I also had the following error on the terminal from which I launched Evince: "fatal internal error -100" eight times, without a newline between the repetitions.
It would be good to find a solution to this problem.