plot2d ([parametric, cos(t), sin(t),[t, -2%pi, 2%pi], [nticks, 8]])$ draws very smooth circle, despite nticks=8.
Oh, some time ago, I updated parametric plots to use adaptive plotting. I think you need to set adapt_depth to something small if you want nticks to have create polygonal approximations.
I have confirmed the above statement:
:lisp (setf (getf plot-options :adapt_depth) 0)
does draw polygonal approximation of a circle.
I have also confirmed that manual is already updated. For the test cases, there are multiple cases where nticks is explicitly specified. I will put some comments in rtest_plot.mac.
It has been committed as [8fafc6].