sisotool() and step() giving different plots in 2017b?

I tried plotting a transfer function using sisotool() and step(), but they give different step diagrams. I tried this in 2017b and 2018 versions of matlab and they give the same result. I found this: https://uk.mathworks.com/matlabcentral/answers/385481-why-do-i-get-an-incorrect-step-response-plot-from-the-control-system-designer but it says the bug should be fixed in 2017b? My code is below:

TF = tf([1,3],[1,4,6,3]);
step(TF);
sisotool(TF);

These are the plots they give:

step():

sisotool:

Thanks for any help.

[Pieter Bunt]

I've the same problem, is this solved?

[Swee Xiao Qi]

I am facing the same problem here, version R2019b

Answer 1

[William Lumme]

Looks like people are having the same problem as I did so I will answer my own question.

step() plots the step response of the given transfer function G.

sisotool() takes the given transfer function and puts it in a feedback loop, so that the new transfer function will be G/(1+G), which will have a different step response. You can see this by looking at the value of "G" under "Controllers and Fixed Blocks" and then clicking on "edit architecture" to see the new system.

I'm not entirely sure this is correct as I just figured it out and haven't thoroughly tested it, but I hope this helps.