Additional points to scatter plot show up at wrong place

Hi everyone,

I have a problem with adding points to scatter plots.
The plot is drawn with the scatterplot() function from the car library:

scatterplot(data[,2] ~ data[,1],
data=data,smooth=F,reg.line=F,xlim=c(0.5,1),ylim=c(0.5,1),ylab="ML",xlab="Freq",cex.lab=1.9,cex.axis=1.8)

after that, I draw one line with abline(0,1,col="gray20") which works
perfectly fine.

now I want to add, say the point (0.6,0.6) to the plot with
points(c(0.6),c(0.6)).
The point is plotted, but not exactly at the proper coordinates, but
at something like (0.55,0.55).

When I use the plot() function to make the scatter plots, this problem
does not occur, but I want to have those nice box plots next to the X
and Y-axes that are drawn by scatterplot()..

Anybody has an idea how to get the points at the right place in the plot?

cheers, Peter