This is probably what I was briefly mentioning in the PM last night.
My game is designed for portrait orientation, full-screen sprites for backdrops (1680x1050) are set to a 90 degree angle. To make things easier I moved the origin in r74 sprite editor to bottom left and then assigned the sprite to position (0,0).
In r75 I sometimes see the sprite lined up properly (filling entire screen) and sometimes it is shifted, as if the sprite's origin was in its center instead of its bottom left. Resetting the origin in r75 sprite editor did NOT resolve this however.