This is working as intended. Elements don't receive events when they're removed from their parent panel. The PR identified as introducing a regression enforced this behavior which was a fix to another bug.
Furthermore, in the repro project, button.clicked and button.RegisterCallback<ClickEvent>() are used as though they were synonymous, but they are not. One always happens before the other, and stopping one doesn't stop the other. Removing an element from its panel between the two should prevent the last of the two from being called.