I found a problem with PM's formatting of Photoshop's resolution data when centimeters is used. Photoshop always expects its resolution value in pixels per inch, even when it is told to display in centimeters. This is different from TIFF resolution formatting and JFIF. I made the change to convert pixels/cm to pixels/inch (multiply by 2.54) and verified that it now works correctly. This fix will be in 4.5.2. Sorry for the inconvenience. For now you can stick with inches and it will work correctly in terms of print size in Photoshop (as long as you don't mind thinking in those units).
BTW - DPI is dots per inch and relates to printing with dots (e.g. ink jet). Pixels per inch or pixels per centimeter is the correct terminology for determining print size based-upon number of pixels.
--dennis