Rick,
Thanks for (creating such a great tool and for) replying and looking into this.
Integer boundaries is understood, and is not the issue I am trying to raise.
What I meant, is that with fixed-ratio it is quite common to start the selection (mouse drag-point) outside the image boundaries, but to still expect that the actual selected pixels will conform to the fixed-ratio.
PDN currently calculates the ratio from the mouse drag-point, instead of from the image start-point.
This leads to the actual selection not being in the correct ratio.
In the screenshot below you can see that PDN describes the selection as 400x400, where in fact the actual pixels selected in the image are not 400x400, and do not conform to the 4:4 ration (no, I don't know why I did 4:4 ratio instead of 1:1 you can make fun of me later).