Re-scaffolding index.php causes SoftException 500 Error

[karol-haltenberger]

SoftException in Application.cpp:261: File "...web/index.php" is writeable by group, referer: https://energiaklub.hu/admin/reports/updates

Re-scaffolded index.php becomes group-writable and the application stops working.
I assume this is caused by the system defaults (php's copy, umask or something like that), but seeing how index.php is required to be not group-writable...the scaffolding process might as well make sure.