1.Import the Fisher's Iris Data.dat in \Samples\Statistic.
2.Highlight all and plot Parallel Index.
3.Double click on the 1st axis, switch to All tab, clear Rescale Each Axis Independently, switch to Scale tab and set From as 6.
==> All From changes to 0
4.Double click on the 1st axis again, set From as 6.
--> Works
5.Active the 1st axis and click Rescale Y button.
==> All From changes to 6, which should be 0

Fixed in Origin 2021.