Server removes group read file permissions

Since updating from 1.20.2 to 1.20.4, the server removes group read permissions from various files upon saving, e.g.:

$ stat -c%A level.dat
-rw-r-----
$ mscs send world save-all
$ stat -c%A level.dat
-rw------- 

In my case this prevents affected files from being backed up by a dedicated backup user.

I don’t see this change documented in the release notes, so I’m not sure whether it’s intentional, if there’s any way to opt out of the new behavior, or if I need to change the backup scheme to accommodate it.

For searchability: POSIX file permissions, mode 600, umask 077