Idle timeout can be changed by typing the number (value is not saved)

In the Screensaver configuration dialog: a new value of 'Regard the computer as idle after' that is typed from keyboard (not by clicking up/down buttons) is not saved.

Steps to reproduce this bug:

1. open the xfce4-screensaver-preferences
2. change value of 'Regard the computer as idle after' by typing it from keyboard (not by clicking up/down buttons)
3. close the window
4. open xfce4-screensaver-preferences again

Expected: value of 'Regard the computer as idle after' changed

What happened instead: value of 'Regard the computer as idle after' not changed

apport-report