[R] ggplot2: ... seem to be overwriting each other

[Eric Fail]

Dear list

A week ago Dennis Murphy helped me out by showing me some nice ggplot2  
tricks . Now I got stuck in a new problem that I can't solve (I have  
ordered the ggplot2-book).

My problem is that I can't add my spline (or geom_smooth) and at the  
same time control the grid (using scale_x_continuous), they seem to  
overwrite each other.

I have continued the working example from my last question (http://n4.nabble.com/add-spline-to-longitudinal-data-preferably-similar-to-SAS-s-I-SM50S-routine-td1017138.html 
)

############ example start ############

tolerance.pp <- read.table("http://www.ats.ucla.edu/stat/R/examples/alda/tolerance1_pp.txt 
", sep=",", header=T)
# install.packages("ggplot2", dep = T)
library(ggplot2)

plot <- ggplot(tolerance.pp, aes(age, tolerance, group = id)) +  
geom_line()
plot + geom_smooth(aes(group = male, colour = male), size = 1, se =  
FALSE)
plot + scale_x_continuous(breaks = c(10, 12, 13, 15))

# plot + scale_x_continuous(limits = c(9, 16))

############ example end ############

I have added the 'plot + scale_x_continuous(limits = c(9, 16)) ' since  
this seem to conflict as well.

Thanks in advance!

Eric