Timeshift backup on btrfs partition fails with error when @home subvolume is included in backup

I installed Kubuntu 21.10 on btrfs partition. By default, it creates @ and @home. I booted into my new Kubuntu btrfs installation, and indeed, I am able to make a Timeshift snapshot, just as "advertised". However, when I try to include @home in the snapshot, I get this error:

Only Ubuntu-type layouts with @ and @home subvolumes are supported

This puzzles me, because this is exactly the layout I have.

sudo btrfs subvolume list /

ID 256 gen 195 top level 5 path @
ID 257 gen 95 top level 5 path @home
ID 283 gen 123 top level 5 path timeshift-btrfs/snapshots/2022-01-07_08-51-33/@
ID 284 gen 148 top level 5 path timeshift-btrfs/snapshots/2022-01-07_09-01-57/@