If someone really relies on the fixed 600x600 dpi resolution of a upp generic printer device, they may possibly not like my suggestion.
Well, but that is how physical dimensions in U++ are defined.
When you are doing output with physical representation (can be e.g. PDF too), it is guaranteed that 1 pixel is equivalent to 1 pixel on 600dpi printer. We call this unit the "dot". Rellying on fixed 600 dpi resolutions seems to be very convenient.
What exactly was the problem? Also, what OS is it? Win32?
I believe anything not really related to Images should print OK, with correct aspect ratio.
As for images, well, pehaps we should not relly on GDI to rescale the image and do it ourselves - that should solve the problem.