unset array[0] doesn't delete the element

[Isaac Good]

Configuration Information [Automatically generated, do not change]:
Machine: i686
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='i686' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i686-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 -march=i686 
-mtune=generic -O2 -pipe -fstack-protector-strong 
-DDEFAULT_PATH_VALUE='/usr/local/sbin:/usr/local/bin:/usr/bin' 
-DSTANDARD_UTILS_PATH='/usr/bin' -DSYS_BASHRC='/etc/bash.bashrc' 
-DSYS_BASH_LOGOUT='/etc/bash.bash_logout' -DNON_INTERACTIVE_LOGIN_SHELLS 
-Wno-parentheses -Wno-format-security
uname output: Linux netbook 4.9.11-1-ARCH #1 SMP PREEMPT Sun Feb 19 14:09:53 
UTC 2017 i686 GNU/Linux
Machine Type: i686-pc-linux-gnu

Bash Version: 4.4
Patch Level: 12
Release Status: release

Description:
        `unset` is broken

Repeat-By:
        $ arr=(1 2 3); unset arr[-1]; echo "${arr[@]}"
        1 2 3