Incorrect fork order

[expe]

(1) Issue/Bug Description:

Left tile gets split before right tile. See video:

Screencast.from.08-09-21.19.35.59.mp4

May be related to #1137

(2) Steps to reproduce (if you know):

Open 3 terminals:

1. First is full screen
2. Second splits vertically - left / right
3. Third splits the left terminal vertically

Window focus doesn't matter - even if I focus another window, the fork order remains the same. I've tried on Wayland and X11.

(3) Expected behavior:

I would expect the right side to split first, such as in the video here: #1148 (review) (but with a horizontal split on the right fork)

(4) Distribution (run cat /etc/os-release):

NAME="Pop!_OS"
VERSION="21.04"
ID=pop
ID_LIKE="ubuntu debian"
PRETTY_NAME="Pop!_OS 21.04"
VERSION_ID="21.04"
HOME_URL="https://pop.system76.com"
SUPPORT_URL="https://support.system76.com"
BUG_REPORT_URL="https://github.com/pop-os/pop/issues"
PRIVACY_POLICY_URL="https://system76.com/privacy"
VERSION_CODENAME=hirsute
UBUNTU_CODENAME=hirsute
LOGO=distributor-logo-pop-os

(5) Gnome Shell version:

3.38.5

(6) Pop Shell version (run apt policy pop-shell or provide the latest commit if building locally):

pop-shell:
  Installed: 1.1.0~1630345490~21.04~0484ffb
  Candidate: 1.1.0~1630345490~21.04~0484ffb
  Version table:
 *** 1.1.0~1630345490~21.04~0484ffb 1001
       1001 http://ppa.launchpad.net/system76/pop/ubuntu hirsute/main amd64 Packages
       1001 http://ppa.launchpad.net/system76/pop/ubuntu hirsute/main i386 Packages
        100 /var/lib/dpkg/status

(7) Where was Pop Shell installed from:

Pop!_OS

(8) Monitor Setup (2 x 1080p, 4K, Primary(Horizontal), Secondary(Vertical), etc):

3440 x 1440 single monitor.

(9) Other Installed/Enabled Extensions: