[pstricks] isotropic XY units in psmatrix?

[Blair Hall]

When I write the following

     \begin{psmatrix}[rowsep=1,colsep=1]
       \dotnode{1} & \dotnode{2} \\
       \dotnode{4} & \dotnode{3}
       \ncline{1}{2}
       \ncline{3}{4}
       \ncline{1}{4}
       \ncline{3}{2}
     \end{psmatrix}

I obtain a rectangular node array, not a square one!

Can anyone tell me why this is not square, and therfore
how I can fix it so it will be.

Thanks

Blair