Tab subtrees are lost when tab tree is moved to new window

Steps to reproduce:

1. Create a tree of tabs by finding a page with a link and then opening the link in a new tab.
2. Collapse the tab group (because, if the close tree behavior generalizes, the tree must be collapsed)
3. Right click on the collapsed group, and "Move Tab to New Window"
4. Observe that the new window only has the root tab, and the original window has no tabs.

Expected behavior:

Ideally, the tab tree moves to the new window, retaining its structure. At the very least, the child tabs shouldn't be lost.

Orion and macOS:

Orion: 0.99.108.1
macOS: 12.0.1