I went ahead and opened a ticket because it does indeed look like a bug. Both Poser 11 and Poser 12 create a correctly sized array of pixels based on the numbers entered in the "Render Dimensions" panel; whatever exports the image file in Poser 12 apparently isn't paying attention to these and calculates its own "physical size" based on the array size and the default number, 72 DPI. This won't affect anybody looking at the image on a monitor, but will affect anybody trying to print.