plot2d - unexpected increase of point size???



I tried this example from the help concerning ploting (xy  -given pairs 
of data points) - Windows 2000, maxima 5.9.13, wxmaxima

 plot2d([[discrete,xy], 2*%pi*sqrt(k/980)], [k,0,50], [style, 
[points,3,5], [lines,,3]], [legend,"experiment","theory"], 
[xlabel,"pendulum's length (cm)"], [ylabel,"period (s)"])$

The line and points are presented, but points are circles (not squares 
as in the picture presented below this code). Moreover, when minimizing 
the plot window to taskbar and again maximizing it, the size of the 
points are almost doubled. Very strange behaviour.

Regards,