When I want to create a background with a rectangle to fill the whole area I use the rectangle tool and draw it.
Then in the inspector I set the x origin coordinate to 0, use tab key to enter 0 for y origin, then tabbing again for setting width and height to be the workspace size.
But as soon I change width/height the former 0,0 xy origin is changed, so i need to set them to 0 again manually.
Step 1, placing rectangle:
Step 2, setting xy origin to 0:
Step 3, setting width of rectangle to be full width which changes x origin:
Step 4, setting height to be full height, which changes now y origin:
The XY origin should stay when I change the width/height of the rectangle, and I suspect this happens to all objects.