Cockpit shows second device in BTRFS RAID1 array as 'unmounted' even though usage is reported properly.

[phol]

Explain what happens

I'm using BTRFS RAID1 as a root filesystem. On boot, /@rootfs is mounted.
Unfortunately, the second RAID1 device of the filesystem is displayed as unmounted
Additionally, Cockpit therefore provides the option to mount it, which I think should be disallowed.

The system has two (sda1, sda2, sdd1, sdd2) MD raid devices for /boot and /boot/efi.
sda3 and sdd3 contain encrypted filesystems, which are part of the BTRFS RAID1 array.

lsblk

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
sda 8:0 0 55.9G 0 disk
├─sda1 8:1 0 1G 0 part
│ └─md127 9:127 0 1023.9M 0 raid1 /boot/efi
├─sda2 8:2 0 1G 0 part
│ └─md126 9:126 0 1023.9M 0 raid1 /boot
└─sda3 8:3 0 53.9G 0 part
└─luks1 253:0 0 53.9G 0 crypt /
sdd 8:48 0 55.9G 0 disk
├─sdd1 8:49 0 1G 0 part
│ └─md127 9:127 0 1023.9M 0 raid1 /boot/efi
├─sdd2 8:50 0 1G 0 part
│ └─md126 9:126 0 1023.9M 0 raid1 /boot
└─sdd3 8:51 0 53.9G 0 part
└─luks2 253:1 0 53.9G 0 crypt

fstab

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>

# / partition
UUID=UUID_3 / btrfs defaults,discard,subvol=@rootfs,compress=zstd:2 0       0

# /boot partition
UUID=UUID_4 /boot ext4 defaults,discard        0       2

# UEFI /boot/efi partition (fat32)
UUID=UUID_5 /boot/efi       vfat    umask=0077      0       1

btrfs filesystem show /

sudo btrfs filesystem show /
Label: none  uuid: UUID_3
	Total devices 2 FS bytes used 2.33GiB
	devid    1 size 53.88GiB used 6.03GiB path /dev/mapper/luks1
	devid    2 size 53.88GiB used 6.03GiB path /dev/mapper/luks2

Version of Cockpit

320-1~bpo12+1

Where is the problem in Cockpit?

Storage

Server operating system

Debian

Server operating system version

12

What browsers are you using?

Firefox, Chrome

System log

No response

[jelly]

Thanks for the issue, this feels related to @mvollmer 's PR #20070 which might improve this situation.