[R] grid.edit problem

[Gabor Grothendieck]

I am having a problem in editing a grob.  It works ok if I try to
shift the grob using npc coordinates but if I do the same thing
using native coordinates the grob disappears.  What is wrong?


library(grid)
grid.newpage()

# create viewport
pushViewport(viewport(xscale = c(100,200), name = "X"))

# draw vertical line
grid.lines(150, 0:1, default.units = "native",  name = "L")

# move line 25% of the way to the right. Works ok.
grid.edit("L", x = grid.get("L")$x + unit(0.25, "npc"))


# but now repeat it shifting it using native coordinates
########################################################

# remove line and draw a new line where the original one was
grid.remove("L")
grid.lines(150, 0:1, default.units = "native",  name = "L")

# move line 25% of the way to the right but use native coordiantes
#### line disappears !!!!!!!!!
grid.edit("L", x = grid.get("L")$x + unit(25, "native"))