[Rd] \U with more than 4 digits returns the wrong character

[Richard Cotton]

If I type a character using \U syntax that has more than 4 digits, I
get the wrong character.  For example,

"\U1d4d0"

should print a mathematical bold script capital A.  See
http://www.fileformat.info/info/unicode/char/1d4d0/index.htm

On my machine, it prints the Hangul character corresponding to

"\Ud4d0"
http://www.fileformat.info/info/unicode/char/d4d0/index.htm

It seems that the hex-digit part is overflowing at 16^4.

I tested this on R3.1.2 and devel (2014-12-03 r67101) x64 under
Windows.  I played around with Sys.setlocale and options("encoding"),
but couldn't get the expected value.

Can others reproduce this?  It feels like a bug, but experience tells
me I probably have something silly going on with my setup.

-- 
Regards,
Richie