PAYRE - hmm, my take on it - Disclaimer - this is my view on it, nothing official.
## Post edited - I decided I didn't explain it well (maybe still haven't)##
As far as I know the vertices are not reporting the actual object position in world space, but the position in relationship the objects own 3D Entity workplane which has nothing to do with the workplane you are currently working on, this is not new, I tested back to v16 and it exhibits same behaviour, again as far as I know - 3D objects have their own (what I call internal workplane), which is whatever plane was active when the object was created.
If you click the 3d polyline and click say vertices 0 in the selection palette, you should see a red dot (may have to zoom out), this dot is on the objects plane, the selection palette reports the vertices in relation to this plane, if you move the object the dot will also move, the way I look at it is - draw a dot on a piece of paper, melt a bit of glue and stick an object on it, move the object and the it stays the same distance from the paper/dot so is reporting like it hasn't moved, if you melt the glue and move the object higher or a different location, the reported vertices will report a different location with respect to the paper/dot, which is essentially what happens when node editing.
In order for the selection palette to report the coordinate required one would need to force some changes to the object so it is on the correct plane, for example as John mentioned node editing.
As I say - just my view and the way I look at workplanes.