${1+"$@"} does not generate multiple words if IFS is empty

[martijn]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: darwin11.4.2
Compiler: /usr/bin/clang
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
-DCONF_OSTYPE='darwin11.4.2' -DCONF_MACHTYPE='x86_64-apple-darwin11.4.2' 
-DCONF_VENDOR='apple' -DLOCALEDIR='/opt/local/share/locale' -DPACKAGE='bash' 
-DSHELL -DHAVE_CONFIG_H -DMACOSX   -I.  -I. -I./include -I./lib  
-I/opt/local/include -pipe -Os -DSSH_SOURCE_BASHRC -arch x86_64
uname output: Darwin breedzicht.local 11.4.2 Darwin Kernel Version 11.4.2: Thu 
Aug 23 16:25:48 PDT 2012; root:xnu-1699.32.7~1/RELEASE_X86_64 x86_64
Machine Type: x86_64-apple-darwin11.4.2

Bash Version: 4.3
Patch Level: 42
Release Status: release

Description:
        The substitution ${1+"$@"} should resolve to "$@" if there is at
        least one parameter -- i.e. one word per parameter. This works fine
        if IFS contains any character or is unset. If IFS is empty, it
        instead resolves to the equivalent of "$*", i.e. a single word
        concatenating all the parameters without a separator. IFS should
        not influence the behaviour of "$@" under any circumstances.

        (d)ash variants, AT&T ksh, mksh, zsh, yash all do this correctly.
        bash 2.05b.13 also does this correctly (!). The bug is present in
        bash 3.2.57 and bash 4.3.42.

        (In bash, ${1+"$@"} is redundant, but in some old versions of ksh
        and other shells, if 'set -u' is active, "$@" throws an error if
        there are no parameters, so ${1+"$@"} is used as a workaround. As a
        result, this is often found in cross-platform scripts. These break
        on bash 3 & 4 if fieldsplitting is disabled by emptying IFS.)

Repeat-By:
        $ IFS=''                        # bug only occurs on empty IFS
        $ set -- this is a test
        $ printf '|%s|\n' ${1+"$@"}     # generates wrong output
        |thisisatest|
        $ printf '|%s|\n' "$@"          # generates correct output
        |this|
        |is|
        |a|
        |test|