r - Second and third Kaplan Meier plots exceeding set x limit -

as can see picture above, second , third kaplan meier curves exceed x-limit , box set.

i used exact same code 3 plots, changing actual survival object each time, y-axis labels , ranges. x-limit , labels same every plot. example of code below:

par(mfrow=c(2,2))  surv.obj <- survfit(surv(start, stop, event) ~ factor(characteristic),     data=dataset)  par( mai=c(2,3,1.5,0.42) )  colours <- c("gray0", "gray75")   # x-axis max( unlist(unname(summary(surv.obj)["time"] )) ) # 1274    plot(surv.obj, mark.time=f, col=colours, lty=1, lwd=2, yscale=100, xscale=1, fun="event",  ylab="", xlab="follow-up (days)", xlim=c(0, 1280), xaxt="n",  axes=f, cex.lab=1.8, cex.main=1.8 )  box("plot", lty=1)  axis(2, cex.axis=1.5, at=c(0, 0.04, 0.08, 0.12, 0.16) ) axis(1, cex.axis=1.5, at=c(0, 300, 600, 900, 1200) ) 

with repeated 2 times next 2 curves.

i know not 'plot specific' code issue, because when plot each 1 separately (and ignore par(mfrow=c(2,2))) produced way want them (with survival curve cut-off @ approx 1280 days). also, tried plotting second , third plots using par(mfrow=c(1,2)) , first 1 turned out fine (which second 1 in plot in picture) , second 1 again exceeded box.

does know why happening , how fix it?

thanks vicki