Comment 5 for bug 330140

No. I think you've slightly misunderstood.
The printer is connected to a windows XP pc.

When I print from across the network duplex works fine when a job is sent from a windows vista PC and a windows 7 PC having tested both.
However, when a job is sent from linux it doesn't duplex even when the duplex options are chosen.
I also tried the new google cloud printing service. The same problem occurs and it doesn't duplex.

Therefore, it seems that the printer happily accepts duplex signals from across the network from other windows PCs but doesn't from anything else.