I am having this problem with a windows 7 HP Elitebook 2540p laptop. Whenever I print a power point presentation on the landscape setting, the first page of the presentation comes out in portrait. This problem only happens when printing to one of our toshiba copiers in color. This is not a problem with a smaller hp color printer also hooked up to the computer.
I have checked the orientation settings and everything seems normal. I have even replaced the laptop with a new formatted one with the most updated drivers. The printers are toshiba 3530 and 2830s.
D'oh - didn't think of double-sided. Perhaps it is a printer problem.
If this only happens in landscape and the previous print jobs have all been portrait, try shipping a blank page of a Word document formatted in Landscape and see if the presentation can follow that and print successfully.