First notification cannot be dismissed and then no subsequent notifications

I'm currently running `sway` on a headless Arch Linux VM under FreeBSD's `bhyve`. There is no video device in this VM, so I'm using the software renderer. I'm currently using the following to start `sway` with VNC access:

```
WLR_BACKENDS=headless WLR_RENDERER=pixman WAYLAND_DISPLAY=wayland-1 sway &
WAYLAND_DISPLAY=wayland-1 wayvnc 0.0.0.0 &
```
I installed the latest versions of everything via the AUR:
```
sway-git r6843.eaeb173a-1
wayvnc-git 0.4.0+16.gead9cdf121-1
wlroots-git 0.15.0.r8.g812951f5-1
mako-git v1.6.r11.gddc1849-1
```

The behavior is the first notification `mako` receives will be displayed, but will not be dismisable regardless of configuration settings. Subsequent notifications will not appear. The only way to get rid of the stuck notification is to execute `killall mako`.