As the tile says, the panel locks up when the context menu (right click menu on an application's panel object in the task bar) is open while any application with an object in the task bar terminates. After it locks up, one can not interact with the panel or anything in it anymore. It changes when a tab is closed and one can change tabs using alt+tab though. Using alt+f4 to close all tabs and then hitting it once again brings up a menu that enables users to log off, reboot, restart, suspend and other things. After the user logs off and logs back in, the panel works again. This is reproducible.
It's still a thing in panel version 4.12.2.
Still a thing in version 4.12.4
This is very likely fixed in 4.13, as reported in Bug 13600. Can you check this version?
Fixed in 4.13.0. Thank you for your time and efforts.