I don't know if I can't remember how but trying to print more than one copy of a 2 sides document doesn't work. I have a duplex capable printer and Indesign send the file, print it on both sides but whatever I do, I just can print one copy. Anybody has similar issues ?
is there a 'Collate' option in your printer specific settings somewhere that you can enable?
I found this option. Still the same problem. Really weird.