On two of our machines with KDE, pressing the logout button on the task bar produces three buttons:
Logout blue button
Turn off Computer red button
Restart Computer orange button
What I have noticed is that pressing the Logout blue button is activated immediately. However, both the red button and the orange button have an additional small white downward pointing arrow to their lieft. Pressing the red or orange buttons lead to activation delays. Pressing the white arrows, on the other hand, produces immediate effects. Not a real problem, just a puzzling effect.
The third machine (with LXDE) exhibits no such difficulty.