Description of problem:

Under the Xfce desktop with xfwm4, if you are Alt-Tabbing between applications and one of the windows closes while the Alt-Tab picker is active, the window becomes 'stuck' and can't be closed or terminated.

The 'stuck' window still appears on the task bar and window list but does not respond and can't be closed. Occasionally after clicking on it you'll get a prompt to terminate the non-responsive window, but it has no effect.

The only way to get rid of the frozen window is to log out of X11. Even killing the parent application won't close its window.


Version-Release number of selected component (if applicable):

xfwm4-4.13.1-4.fc29.x86_64

How reproducible:

Always.


Steps to Reproduce:
1. Open a Terminal window and run: `sleep 5 && exit` to make the window close after a few moments.
2. Hold the Alt-Tab key buttons to make the window switcher appear. Keep the keys held until the Terminal window closes.
3. After the window tried to close, it in fact sticks around and doesn't respond and can no longer be closed or terminated.

Actual results:

The window that closed during the Alt-Tab sticks around on the task bar and window switcher.


Expected results:

The window that closed should disappear from the task bar and window switcher.


Additional info:

I first saw this when sending an e-mail on Thunderbird: I clicked 'send' and alt-tabbed away to do other work, and the Compose Email window tried to close while the Alt-Tab menu was active, and the window instead stuck around frozen. Killing Thunderbird completely did not take away the frozen window.