latex knitr chunk echo=FALSE disrupts par() setting - knitr

Question

I'm new to latex and knitr and have an issue with the output from an R chunk when I use echo=FALSE. The .Rnw code below works as expected i.e. the output has
1. some code
2. a block of figures arranged 2 x 3
3. some more code
4. a block of figures arranged 2 x 3
However changing the chunk opening to eliminate the code block from the output
<<bghist2_mas_rma, fig.height=4, fig.width=6, echo=FALSE>>=
not only removes the code from output (good) but also over-rides the par() setting such that the two figures (each of 2 x 3) are placed adjacent on the page, with most of the second falling off the edge.
Other than simply leaving the code in the output how could I get around this?
thanks
B
\newpage
<<bghist2_mas_rma, fig.height=4, fig.width=6, echo=TRUE>>=
par(mfrow=c(2,3))
for(i in 1:6){
hist(bg.mas[,i], xlab="", las=1,
main=paste(sep="", "bg.mas[, ", i, "]"),
xlim=c(-100, 300), breaks=10000)
}
par(mfrow=c(1,1))
par(mfrow=c(2,3))
for(i in 1:6){
hist(bg.rma[,i], xlab="", las=1,
main=paste(sep="", "bg.rma[, ", i, "]"),
xlim=c(-100, 300), breaks=10000)
}
par(mfrow=c(1,1))
#

Answer 1

The simplest solution is to split them into separate chunks:
<<bghist2_mas_rma, fig.height=4, fig.width=6, echo=FALSE>>=
par(mfrow=c(2,3))
for(i in 1:6){
hist(bg.mas[,i], xlab="", las=1,
main=paste(sep="", "bg.mas[, ", i, "]"),
xlim=c(-100, 300), breaks=10000)
}
#
<<bghist2_mas_rma_2, fig.height=4, fig.width=6, echo=FALSE>>=
par(mfrow=c(2,3))
for(i in 1:6){
hist(bg.rma[,i], xlab="", las=1,
main=paste(sep="", "bg.rma[, ", i, "]"),
xlim=c(-100, 300), breaks=10000)
}
par(mfrow=c(1,1))
#