Just write a test with GdipDrawImageI and scenario described above and you will see the problem. In my case it's even more visible because of indirect magnifaction: image with resolution 100 dpi is being copied to device with 300 dpi.
I just did, and the behavior, though it looks wrong, is the same between builtin and native - the image is shifted by 1/2 pixel so that it's cut off at the upper-left and we have extra transparent space at the lower-right.