pkexec command line from a Launcher no longer works

To reproduce:

1. Make a launcher on a panel that has a command line like pkexec nemo %U or pkexec thunar to run a GUI program as root
2. Click that launcher

Current behavior:

The program doesn't run. Nothing seems to happen.

Expected behavior:

The program is expected to run and display its GUI on-screen.

Additional information:

Before updating from XFCE 4.14 to 4.16, this issue was not present. I was able to run nemo as root with pkexec nemo %U in a launcher. The same is the case for thunar. I also was able to run checkra1n as root with pkexec checkra1n --gui in a launcher. This proves to me that it's not a bug with nemo or thunar.

I found a similar bug report here, for the garcon menu: garcon#18 (closed) . It seems the garcon menu bug report was closed as fixed recently. Maybe something similar affects XFCE panel launchers.

I'm not sure if XFCE panel launchers have their own issues list. I searched for one first and couldn't find it. I apologize if this report was posted in the wrong list. If that's the case, please direct me to the correct place and I will report this there.