Why does R start in wrong working directory despite R_USER setting?

Hi
After launching newly-installed R 3.2.1 (on Windows 7), I run the following two commands:

getwd()[1] "C:/ProgramData/Microsoft/Windows/Start Menu/Programs/R"
Sys.getenv('R_USER')[1] "C:\\Users\\<my username>\\Documents"

I would like the startup working directory to be that pointed to by R_USER.
I don't have administrative access to the machine.
Many thanks for any insight anyone can provide.
Mauricio