[R-sig-Geo] readGDAL loses datum

[Oliver Soong]

R 2.15.1 32-bit, rgdal 0.7.20, Windows 7.

grid <- GridTopology(c(-2100000, 1200000), c(100, 100), c(1, 1))
p4s <- CRS("+proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23 +lon_0=-96
+x_0=0 +y_0=0 +datum=NAD83 +units=m +no_defs +ellps=GRS80
+towgs84=0,0,0")
img1 <- SpatialGridDataFrame(grid, data.frame(band1 = 1), p4s)
img1.file <- file.path(tempdir(), "img1.tif")
writeGDAL(img1, img1.file)
img2 <- readGDAL(img1.file)
img2.file <- file.path(tempdir(), "img2.tif")
writeGDAL(img2, img2.file)
img1 at proj4string
img2 at proj4string

For me, img1 at proj4string has +datum=NAD83 and img2 at proj4string does
not.  Not surprisingly, if I look at both files in Arc, img1 has a
defined datum and img2 does not.

Am I doing anything wrong?

Oliver