"! true &" sets $? to 1

[Vincent Lefevre]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-pc-linux-gnu' 
-DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL 
-DHAVE_CONFIG_H   -I.  -I../. -I.././include -I.././lib  -D_FORTIFY_SOURCE=2 -g 
-O2 -fstack-protector-strong -Wformat -Werror=format-security -Wall
uname output: Linux xvii 3.11-2-amd64 #1 SMP Debian 3.11.10-1 (2013-12-04) 
x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 4.3
Patch Level: 24
Release Status: release

Description:

When a pipeline starting with "!" is run in background, bash sets $?
to 1 instead of 0. POSIX says:

  The exit status of an asynchronous list shall be zero.

in 
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_03_02

Note that other shells (dash, ksh93, mksh, zsh) behave correctly.

I've also reported the bug in the Debian BTS:

  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=758969

Repeat-By:

vinc17@xvii:~$ ! true &
[1] 15171
vinc17@xvii:~$ echo $?
1
[1]+  Done                    true