Compositor crashes after closing stacked window

[Wasabi375]

The setup for this crash is a bit elaborate and there might be easier ways to reproduce this, but this is how I can reproduce this. I assume this is reproducible with any program that can spawn child windows, but I only have Thunderbird to test with right now.

0. Select Tiling mode
1. Launch Thunderbird
2. Open a new window using the "New Messages" window.
3. Maximize the "New Message" window
4. On a second monitor open any window (I used Files for testing)
5. Drag Files onto Thunderbird until the "Stack Windows" panel is visible and then release
6. Close the Stacked Finder Window using the keyboard shortcut.
   6.5. This should close "Files" but also seems to mess up the tiling layout. The "New Message" window now takes up only half the screen, with half the screen showing the background image.
7. Without changing focus use the "Close window" keyboard shortcut.
8. At this point the compositor crashes and the cosmic-session is restarted

Here are some images I took of me reproducing the crash. I had to take those using my phone, because the screenshot tool would either cancel the actions or crash the compositor after step 6.

Create the stacked windows:

The stacked windows

The messed up tiling layout:

I am using nixos-unstable and have the following cosmic packages installed

cosmic-applets-1.0.0-beta.5
cosmic-applibrary-1.0.0-beta.5
cosmic-bg-1.0.0-beta.5
cosmic-comp-1.0.0-beta.5
cosmic-conductor-v0.2.1
cosmic-edit-1.0.0-beta.5
cosmic-fallback-themes
cosmic-files-1.0.0-beta.5
cosmic-greeter-1.0.0-beta.5
cosmic-greeter.conf
cosmic-greeter.pam
cosmic-icons-1.0.0-beta.5
cosmic-idle-1.0.0-beta.5
cosmic-initial-setup-1.0.0-beta.5
cosmic-launcher-1.0.0-beta.5
cosmic-notifications-1.0.0-beta.5
cosmic-osd-1.0.0-beta.5
cosmic-panel-1.0.0-beta.5
cosmic-player-1.0.0-beta.5
cosmic-randr-1.0.0-beta.5
cosmic-screenshot-1.0.0-beta.5
cosmic-session-1.0.0-beta.5
cosmic-settings-1.0.0-beta.5
cosmic-settings-daemon-1.0.0-beta.5
cosmic-term-1.0.0-beta.5
cosmic-wallpapers-1.0.0-beta.5
cosmic-workspaces-epoch-1.0.0-beta.5