Trace displays for x-slider movements but not y-slider

[psychemedia]

If I define a simple world:

from jyro.simulator import Pioneer
from jyro.simulator import VSimulator

robot_name = "Pioneer"
robot = Pioneer(robot_name, 5, 5, 0)

def world(sim):
    # Bounding box around the simulated world
    sim.addBox(0, 0, 10, 10, fill="backgroundgreen", wallcolor="lightgrey")

VSimulator(robot, world);

then check Trace Path in the simulator, if I move the x-slider the trace line is drawn, but if I move the y-slider, whilst the robot is moved, the line is not drawn.

(Doug, I will try to submit PRs, but for now I need to get on with just trying to crank out some activities to demo to others on my module team with whatever's to hand; I'll log issues here as I come across them, or if you'd rather keep things from getting cluttered here, I can post them to a fork of this repo.)

[dsblank]

Weird... will check.