Split command documentation is here: https://docs.mcneel.com/rhino/6/help/en-us/commands/split.htm
It says: When you split a surface with a 3-D curve in an angled parallel or a perspective view, the cutting curve is pulled onto the surface by closest points.
This is not true. If the curve is 3-D curve (its bounding box is a solid), and the view is perspective, the Split command fails.
The Split command documentation does not explain what happens when the curve is straight line and the view is perspective. (The line is projected toward construction plane.)