Cairo png device not working in R 3.2.1 on OSX

The cairo png device on R 3.2.1 gives a warning "Application built with
libpng-1.5.18 but running with 1.6.17" and then produces a completely blank
png image.

if(isTRUE(capabilities()[["cairo"]])){
  options(bitmapType = "cairo");
}

png(tmp <- tempfile())
plot(cars)
dev.off()
system2("open", tmp)