[Users] Claws release 4.1.0, group mail sharing disabled

[mnieuw at zap.a2000.nl]

This is how I can reproduce the error.

1. Environment
- System: Mint 20.3, mounted as /dev/sda5 ext4 rw,relatime,errors=rem .
- Data partition: mounted /mnt/DataLinux /dev/sda7 ext4
rw,nosuid,nodev,noexec
Note that the data partition is mounted "noexec", don't know if that is
relevant.
- Mail folder /mnt/DataLinux/Mail
- Drafts properties->general "folder chmod" set to 660 .

2. Steps to reproduce:
Open Claws 4.1.0, Compose new message
From: automatically filled with my email address
To: leave empty (we leave this field empty until ready to send, to
prevent accidental sending of an incomplete msg)
Subject: "test draft sharing"
Body: "text"

click "Draft" , msg window disappears, and msg shows up in
"Drafts" folder, and is readable there.

From a terminal, I do ls -lrt /mnt/DataLinux/Mail/draft/ . It shows:
-rw------- 1 mat homeusers     408 Apr 14 10:18 280

Note that the groups rw is missing, 

Hope this helps, else I can probably debug (after Easter).

Mat