write.csv causes system() and ? to stop working

I have a large (100MB, 940k lines) csv file.  If I run

g <- read.csv('combineTfe-dataFrame-TD.dat')
write.csv(g, file="tmp.data");

Now ?mean returns without printing anything to screen and
system("touch test.dat") does nothing.

If instead I just write out the top of the data, as in

g <- read.csv('combineTfe-dataFrame-TD.dat')
tmp = g[1:100,]
write.csv(tmp, file="tmp.data");

?mean and system("ls") have the expected beviour.

This is on an AMD64 machine running Ubuntu,  under both R 2.6.2 and
2.7.1 (a fresh install).  The same minimal code works fine on a
different (x86) machine.

Any help will be greatly appreciated.

thanks,
Scott