why draw the plot this way?

There's a bug in Matlab's Bode plotter?

Have you tried doing it manually? I.e. get the frequency response into a vector, then plot the vector's amplitude and phase vs. frequency?

Although I haven't done it manually, I have a chart on the Modern Control Engineering, 3rd Edition, Ogata. The illustration on it is just what I stated in my last post. the nonminimum phase counterpart's phase may also begin in approximately 0 deg and end at -180 deg. I do not know why Matlab begin with 180.

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(1-jwT)=3D> fourth quadrant =3D> 270 270-90

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