I just tried this in 3 different releases of Print-Tool including the latest release.
Am I doing something wrong please ?
Configuration of Custom Paper Size:
http://www.kennethleegallery.com/images/forum/printtool1.jpg
Print Settings with 8x10 print:
http://www.kennethleegallery.com/images/forum/printtool2.jpg
Resulting Image:
http://www.kennethleegallery.com/images/forum/printtool3.jpg