Null created by Trim Paths does not function properly in 3D Space

I have an arrow moving along an extended path using a trim paths operator and a trace path null.  I would like to track the arrowhead (linked to the end of the stem by parenting to the trace path null) as it moves through 2D space.  Only way to do that that I know of is to use a camera to track the arrowhead as it goes off the confines of the original comp,  so I need layers to be 3D.  Fine, I make the layers 3D. Now suddenly the trace path null is thousands of pixels back in Z space.  One screenshot shows where the trace path null populated the moment I turned it into a 3D layer.  No clue why this happens, but I figured I could make a corrective null to counteract that move and get it back to the correct position (new null, parent TP null to new, move new null to correct z pos).  This brings the arrowhead to the correct z position, but when I try to move the camera with the arrow no dice. The arrowhead lags behind, still moving forward, but much slower than the top of the stem as soon as the camera begins to move (shown in other screenshot).  Why? This seems like either a bug or a serious limitation of the trace path function. Any suggestions would be appreciated.