photosmart premium c309 will not duplex

I recently purchased a new printer because I need the duplex feature and when I first installed it it worked fine, both sides in the same direction. I have recently had to erase and reinstall snow leopard along with all my drivers, software and applications. Now I cannot get the duplex to print the second side in the same direction as the first, it automatically inverts it so that it is upside down. I have tried ticking and unticking in turn the collation button and the reverse page orientation to no avail, each time the printer prints the second side upside down. I have been in touch with both hp to reinstall the drivers from scratch and with apple to delete the whole programme and start again but still no joy, can anyone help? This was the only reason for purchasing a second printer!