[R] Plot difference between PNG and X11

[Al Piszcz]

I am rendering a plot using boxplot, mtext, abline, etc.

The X11 view of the plot looks correct.

When I change to the png device to:
  png(filename="bxplot.png",width=640,height=640)

I get half of a character label plotted in the lower left
corner in the resulting .png file.
The character fragment started to appear in png when
I started using mtext.

mtext(labelvector,side=1,at=c(xi,0),line=2)

Any thoughts on items to try? Thx.