grid stringHeight

Dear all,

I'm puzzled by the behavior of stringHeight in the grid package.
Consider the following test,

library(grid)

test<- function(lab="dog", ...){
   g1<- textGrob(lab)
   g2<- rectGrob(height=grobHeight(g1), width=grobWidth(g1))
   gg<- gTree(children=gList(g1,g2), ...)

   print(c("height:", convertUnit(stringHeight(lab), "mm", "y")))
   grid.draw(gg)
}

grid.newpage()
test()
test(expression(dog), vp=viewport(x=0.6))
## notice how the dog's tail is being cut off, where
## expression yields a snug cage

grid.newpage()
test("aoc")
test(expression(aoc), vp=viewport(x=0.6))

It appears that stringHeight correctly calculates the height for an
expression, but not for a basic string. I think it used to produce the
same output for both.

Best regards,

baptiste

sessionInfo()
R version 2.13.0 alpha (2011-03-27 r55076)
Platform: i386-apple-darwin9.8.0 (32-bit)

locale:
[1] C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  grid      methods
[8] base