[R] x-axis in filled.contour

[Thomas Steiner]

The filled.contour function gives me some strange output. What did I do wrong?

x=seq(0,1,length=10)
y=seq(0,1,length=10)
z=array(rnorm(100),dim=c(10,10))
filled.contour(x,y,z)
lines(0.4,0.8,type="p")
abline(v=0.4,lty="dashed")

the x-cooridnate of the line and the point is 0.4, but it's slightly
above. This problem just appears with "filled.contour", so I guess
there is a problem with the key on the right.
I use 2.4.0 under unbuntu
Thomas