When tvtime is running, Shift_L KeyPress and KeyRelease events are generated every 30 seconds. They pop up in the window with the keyboard focus. This is very annoying when doing work in parallel to running tvtime. For example, when searching backwards in a file with vim, the search direction is silently reversed, though the physical Shift_L key is pressed all the time. (vim searches backward with the 'N' character and forward with the 'n' character.) Or, when typing an all upper case symbol, the case changes to lower case in the middle of the symbol, though the physical Shift_L key is pressed all the time. These effects feel like being random due to their 30 seconds interval.
The most obvious way to see the problem is to start the utility 'xev'. Activate the xev window to give it the keyboard focus. When tvtime is running, you can see the events appearing every 30 seconds. When you stop tvtime, the events stop to appear. If you start tvtime again, the events happen again.
This is tvtimes way to disable the screensaver. It is the most stupid and annoying way to do it (ok, pseudo pressing "tvtime is cool" would be more annoying). Other programs do that differently (for example kaffeine which I use for dvb). I change the severity because it makes the package unusable when doing anything else then watching tv.
A better way is to use xss to reset the xscreensaver timer.
Lubos Lunak <firstname.lastname@example.org> informed me that it is better to still use XResetScreenSaver for screensaver which ignores the X internal timers like the ones from KDE since rev916966. I tested it with enabled dpms and kde different screensaver types and it works fine.