Multi-device btrfs filesystem filesystem should be aggragated into a single volume.
Specifically, XFCE is calling get_mount() on volumes, looking to see if a given device can be mounted. This causes some icons to be displayed on the desktop for devices that are already mounted.
When enumerating volumes, devices detected as btrfs should be skipped if /dev/disk/by-uuid/${UUID}
does not link back to the devices being scanned. This should cause only a single volume to be enumerated per mountable btrfs "filesystem filesystem."