Thank you for the hint. But:
We are using ppi (pixel per inch) as unit for resolution. Pixel per centimeter is totally unusual. But we use centimeter as unit for the width of prints ... If I change the preferences to centimeter, the unit for the resolution will change to centimeter per inch.
i think the problem could be solved, if you add centimeter to the pulldown in "Save Photo as ..." The unit for the resolution should stay at ppi.
Christoph