Repeatedly plotting the same point causes weird extra lines

[LaCuneta]

Suppose you have a model with a single plot called test and a button for setup and a forever button for go:

to setup
  clear-all
  set-current-plot "test"
  create-temporary-plot-pen "ziggy pen"
  set-current-plot-pen "ziggy pen"
  reset-ticks
end

to go
  set-plot-pen-color red + 2
  ifelse ticks < 5 [
    plotxy 0 0
  ] [
    plotxy (ticks / 2) (ticks + random ticks)  
  ]
  tick
end

It should create a nice jagged line climbing up and to the right. It kind-of does but it also generates weird random lines back to point (0, 0).

A few notes on the behavior:

• If you avoid repeating the plotxy 0 0 and only do it once, the extra lines do not appear.*
• If you do not set-plot-pen-color on every tick the extra lines do not appear (!?).*
• It doesn't matter which point you choose to repeat, if you do plotxy 2 2 instead of plotxy 0 0 you'll get the same behavior.
• If you export the model state with the extra lines and then import it back the plot will appear correct without the extra lines until you hit go again.

*Either or both of these are probably the best workarounds for this issue.