Two sides printing doesn't work on my HP Photosmart C3180. The option
gets ignored (the printer prints the whole sequence and there is no
GUI asking for page reinsertion).
As far as I can tell from its specifications the C3180 does not have
auto-duplex. auto-duplex is when the sheet of paper is pulled back into
the printer, turned round and printed on the other side.
I was under the impression that two sides printing wasn't auto-duplex
but manual two sides printing (that is, first printing even pages,
then reversing them manually and then printing odd pages on the
reverse). I seem to remember there were further options for this. If I
was mistaken, please forgive me.