From the same standpoint, btrfs is not sane either. You cannot dd it to a different block device, even when unmounted. When the kernel sees two btrfs filesystems with the same UUID on two different block devices, it thinks they are one filesystem, and corrupts both.
The difference is that you can easily edit the UUID of a btrfs filesystem with `btrfstune -U` immediately after making the copy so the filesystems are unique again. You need to do this anyway if you have mount rules based on the UUID, regardless of the filesystem type, or you run the risk of mounting the wrong device. It is also possible to tell btrfs which devices make up a particular filesystem with the device= mount option, which ought to bypass the default grouping based on the UUID.
Can one wait indefinitely before running `btrfstune -U`? The "immediately" in your comment makes it sound like a racy/flaky workaround, assuming you are referring to immediacy in time.
You can wait until just before the next time the device is scanned for filesystems, or perhaps when the next btrfs filesystem is mounted. Beyond that it will start to cause problems.
