[Gnuplot-bugs] sin(x^2-y^2)

First thanks for this excellent tool. I use it in class to show graphs
to students.

When I do a contour plot of this, I see circles and I should see hyperbolas.

gnuplot> set contour
gnuplot> splot sin(x**2 - y**2)


       G N U P L O T
       Version 4.2 patchlevel 4
       last modified Sep 2008
       System: MS-Windows 32 bit

Note I also tried this in Ubuntu Intrepid 64 bit and saw the same issue.

sin(x^2 - y^2) = k for |k| leq 1

x^2 - y^2 = arctan(k) --another constant

The graphs is confusing so I can't say if it is wrong. When I tried
this function in maple I saw the hyperbolas as expected.

Thanks,

Karim