emergeのconflictについて

!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

dev-python/pluggy:0

(dev-python/pluggy-0.5.2:0/0::gentoo, ebuild scheduled for merge) pulled in by
<dev-python/pluggy-0.7s[python_targets_pypy(-)?,python_targets_pypy3(-)?,python_targets_python2_7(-)?,python_targets_python3_4(-)?,python_targets_python3_5(-)?,python_targets_python3_6(-)?,-python_single_target_pypy(-),-python_single_target_pypy3(-),-python_single_target_python2_7(-),-python_single_target_python3_4(-),-python_single_target_python3_5(-),-python_single_target_python3_6(-)] required by (dev-python/sqlalchemy-1.2.7:0/0::gentoo, ebuild scheduled for merge)
^ ^^^^

(dev-python/pluggy-0.7.1:0/0::gentoo, ebuild scheduled for merge) pulled in by
>=dev-python/pluggy-0.7[python_targets_pypy(-)?,python_targets_pypy3(-)?,python_targets_python2_7(-)?,python_targets_python3_4(-)?,python_targets_python3_5(-)?,python_targets_python3_6(-)?,python_targets_python3_7(-)?,-python_single_target_pypy(-),-python_single_target_pypy3(-),-python_single_target_python2_7(-),-python_single_target_python3_4(-),-python_single_target_python3_5(-),-python_single_target_python3_6(-),-python_single_target_python3_7(-)] required by (dev-python/pytest-3.10.1:0/0::gentoo, ebuild scheduled for merge)
^^ ^^^

https://wiki.gentoo.org/wiki/Troubleshooting/ja

公式のHandbookを読んで、コンフリクトが起きた場合は、

コンフリクトを起こしているパッケージを

「--oneshot」オプションで入れてしまうとコンフリクトを解決しやすいと書いてあったので、

sudo emerge -a -1 =dev-python/pluggy-0.5.2

でemergeしようとしたところ、

zsh: dev-python/pluggy-0.5.2 not foundというエラーが出て終わってしまう。

仕方がないので、bashに切り替えて再度実行したら、エラーも出ずに正常終了した。なぜだろうか？

bash と zsh だと何か違うんだろうか？わからない・・・