SimpleMove not working on Y axis?

I’m trying to use SimpleMove to move a character around 3D space, but the character only seems to move on the X&Z axes. Even though the Y component of the vector I pass to SimpeMove is non-zero, the character never moves on the Y axis. Does SimpleMove just not allow Y axis movement or is there some flag I need to set to allow it?

SimpleMove() ignores Y-axis.