R devel - May 2016 - R devel: install.packages(..., type="both") not supported on Windows

Is the following intentional or something that has been overlooked?

[HB-X201]{hb}: R --vanilla

R Under development (unstable) (2016-05-13 r70616) -- "Unsuffered
Consequences"
Copyright (C) 2016 The R Foundation for Statistical Computing
Platform: x86_64-w64-mingw32/x64 (64-bit)

[...]

## Note that "source" is the built-in default
> getOption("pkgType")
[1] "source"

## Trying with 'both'
> install.packages("MASS", type="both")
Installing package into 'C:/Users/hb/R/win-library/3.4'
(as 'lib' is unspecified)
Error in install.packages("MASS") :
  type == "both" can only be used on Windows or a CRAN build for Mac
OS X

## But 'win.binary' works
> install.packages("MASS", type="win.binary")
Installing package into 'C:/Users/hb/R/win-library/3.4'
(as 'lib' is unspecified)
trying URL
'https://cran.r-project.org/bin/windows/contrib/3.4/MASS_7.3-45.zip'
Content type 'application/zip' length 1088567 bytes (1.0 MB)
downloaded 1.0 MB

package 'MASS' successfully unpacked and MD5 sums checked

> sessionInfo()
R Under development (unstable) (2016-05-13 r70616)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

locale:
[1] LC_COLLATE=English_United States.1252
[2] LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C
[5] LC_TIME=English_United States.1252

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

/Henrik