Actually, This is kinda weird... I have been having problems placing items in the exact spot since the update... Re-run your project and click on the Project folder and change the Fullscreen in browser setting to off.(on the left).
You should now see it center a bit better, but it is still off... I made the window and layout 800x600 and a sprite at 800x600 and when I center it as you state above it is about 1/2 inch to the right and down... This may be a BUG... anyone else want to verify this on their own?