Paper white IS white. 
Your correct of course Andrew, but I believe my point is also valid. As far as most inkjet printers are concerned Absolute white is indeed NOTHING, in the sense that there's nothing there to print, the same as the transparent half of the image. And of course not all papers have a White surface to print on, at least certainly not pure white. But of course in that case the reference to pure white must be defined. My reason for stating it in that manner was to make sure the OP is aware that his printer is NOT printing white, it is actually printing nothing. However, in his case it would seem that his situation is an exception. I'm interested to see if he does do the experiment I suggested and the outcome. If the half filled with white shows any degree of density compared to the transparent half I believe it could perhaps be either a profile or a printer setting issue.
Gary
