strange journald *.journal file permissions

[Vincent Lefevre <vincent@vinc17.net>]

Can anyone explain these strange journald permissions?

-rw-r-x---+ 1 root root            16777216 2015-07-05 12:57:55 system.journal*
-rw-r-x---+ 1 root systemd-journal  8388608 2015-07-05 12:17:21 user-1000.journal*

More precisely, why the bit x for the group?

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Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)