I'm using KDE 4.10.1.

What configuration options/files are responsible for controlling screen saver behavior?

I saw the discussion and patch in bug report 310871. That patch was applied in 4.10.1.

In System Settings -> Display and Monitor -> Screen Locker, I selected the "Screen saver" button. Regardless of the delay time I configure, when the time expires the Simple locker appears and the screen saver never kicks in.

I tested the screen saver with a test account. There the screen saver behaves much like the discussion in the bug report. That is, the Simple locker momentarily appears and then the screen saver kicks in. With my normal account the Simple locker appears but the screen saver never kicks in.

The kscreensaver file does update when I make changes in System Settings. Here is a copy of the file:

[ScreenSaver]
Enabled=true
LegacySaverEnabled=true
Lock=false
LockGrace=60000
PlasmaEnabled=false
Saver=asciiquarium.desktop
Timeout=600

I tested changing options in Power Management but they do not seem to be affecting the screen saver problem. The result is always the same with the Simple locker appearing and no screen saver.

Any ideas?

Thanks.

Have you tried using a different screen saver in case the one you are trying to use currently is crashing (or otherwise failing to start) for some reason?

Yes, thank you, I have tested several screen savers from different categories.

One odd observation is once in a while the screen saver does activate, although much of the time not. I can't replicate the behavior with the testing accounts, where the screen saver activates all the time.

Edit: I seem to have stumbled across the cause. Whenever desktop effects are enabled the screen saver will not activate. When I disable the desktop effects with Alt-Shift-F12, then the screen saver activates. Enable the desktop effects and the screen saver stops activating with only the simple locker showing.

I found the exact cause. In System Settings -> Desktop Effects -> Advanced, is a check box option "Suspend desktop effects for fullscreen windows." When enabled the screen saver does not activate. When disabled the screen saver activates as expected. This check box controls kwinrc [Compositing] UnredirectFullscreen. There is no respective help for the check box.

The check box probably was enabled on my system through curiosity learning about the various desktop effects. I filed bug report 317156 to address certain related issues.