So they're both anchored to the center, and are in essence positioned in fixed places on the screen. When your screen size changes, they appear to "move" -- while in fact they stay in the same spot, it's your screen size that moves.
You need to use anchors correctly. Check the first example. Build it for iPad. See how it changes and note how the buttons stay in corners. Tilt the iPad. Watch how the center-aligned dialog box now gets cut off, but the buttons still remain in the corners.