Window dimensions inconsistent when using tiling on Wayland

Instead of restoring to the previous window size, Mutter seems to shrink the window dimensions by a fixed factor each time a window is tiled and then restored (Super+Down), as can be seen in this video. What is happening is just that I am tiling windows using Super+(arrows) shortcuts. Expected behaviour would be having the "old" window size after restoring from each type of tiling.