Error with strwidth after lattice graphic drawn

In

platform i386-pc-linux-gnu
arch     i386
os       linux-gnu
system   i386, linux-gnu
status
major    2
minor    0.1
year     2004
month    11
day      15
language R

I'm getting an error when using strwidth after a lattice graphic is drawn:

library(lattice)
xyplot(runif(20) ~ runif(20))
strwidth('xxx')

Error in strwidth("xxx") : invalid graphics state

Any help appreciated.  I have version 2.0.1 of grid and version 0.10-14 
of lattice.

Frank E Harrell Jr   Professor and Chair           School of Medicine
                      Department of Biostatistics   Vanderbilt University