Ringing, over/undershoots come from the mismatch of reactive
components / aspects to the resistive sources & terminations.
From what is shown, these are all ideal. So it's not surprising
there are no nonideal behaviors.
As a test, try skewing the termination resistance from the ideal
value. At (say) 2X or 1/2X you should see significant overshoot
(high Zterm) or staircasing (low Zterm).
I am unfamiliar with the mtline element, have only used the
simple tline. Maybe there's more to it. But I'd start with the
simple look at whether termination resistor value matters
(it had better) as a sanity check.