plotdf questions: tstep, Runge-Kutta and singular points

Hi there,

I have some problems with plotdf command. I'd like to plot some nice
phase portraits of singular points. However, it seems that integration
algorithm becomes inaccurate near singular points (e.g. nodes).

Here is an example.

plotdf([x**2-y,log(1-x+x**2)-log(3)],[x,1,3],[y,3,5]);

The output looks like this:

http://schurov.com/maximassode.png

One can see artifacts near the singular point.

I tried to overcome this issue by setting tstep parameter as described
in the docs (http://maxima.sourceforge.net/docs/manual/de/maxima_66.html).
However, it seems that the system simply ignores tstep parameter. At
least, I tried commands

plotdf([x**2-y,log(1-x+x**2)-log(3)],[x,1,3],[y,3,5],[tstep,100000]);

and

plotdf([x**2-y,log(1-x+x**2)-log(3)],[x,1,3],[y,3,5],[tstep,0.000001]);

I believe that the first command should give very inaccurate picture,
and the second one have to produce much more accurate pictures. In
fact, they are identical to each other. Note also, that I do not have
"tstep" parameter in the "Plot setup" window.

The other idea was to switch to Runge-Kutta method. The docs says it's
possible ("The Adams Moulton method is used for the integration; it is
also possible to switch to an adaptive Runge-Kutta 4th order method"),
but I didn't found such an option in the options list.

Version of my Maxima:

Maxima 5.29.1 http://maxima.sourceforge.net
using Lisp SBCL 1.0.55.0.debian

Any ideas?

--
With best regards,
Ilya V. Schurov.