Orthello Sprite Depth inconsistent for large levels

Hello,

I am making a 2D game using the Orthello framework. I have a character moving through an orthographic top down Tiled-based level, the level at depth 0 and the character on depth -1. The level itself is large, 2048 by 2048 pixels long. I've noticed that in certain places, the character will actually sink below the ground even I am moving the character nothing in the z axis. Even moving the sprite around in the scene editor changes the Z axis when I am only changing X and Y. Does anyone know why this occurs? This does not happen with normal planes and orthogonal cameras.

I have also tried forcing the y-axis to remain constant, but the character still jumps layers as it goes too far north or south (z axis).