'mapfile -O1 array' breaks '[[ -v array ]]'

[Wiley Young]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -O2 -flto=auto -ffat-lto-objects -fexceptions -g
-grecord-g>
uname output: Linux localhost-live 6.0.7-301.fc37.x86_64 #1 SMP
PREEMPT_DYNAMIC>
Machine Type: x86_64-redhat-linux-gnu

Bash Version: 5.1
Patch Level: 16
Release Status: release

Description:
        When an array 'a_foo' is created with 'mapfile -d '' -t', it is
tested with '[[ -v a_foo ]]' and '[[' returns 0. When '-O 1' is added to
mapfile, '[[ -v a_foo ]]' returns non-0.

Repeat-By: In test 3, when declare shows array "y" exists and has indices
beginning at 1, "[[ -v" shows array "y" doesn't exist.

I=1
for AB in '' "-O1"; do
  for CD in '' a_quux; do
    :;:;:
    printf '\nloop %d\n' $(( I++ ))
    unset a_quux a_foo
    a_quux=( x y z )
    mapfile -d '' $AB -t a_foo < <( printf '%s\0' "${a_quux[@]}" )
    [[ $CD == a_quux ]] && a_foo+=( [0]=workaround )
    declare -p a_foo
    [[ -v a_foo ]]
    printf 'exit: "[[ -v": %d\n' $?
  done
done

Thanks,
Wiley