Hi,
the workaround by disabling DDC/CI in the monitor OSD setup works for me.
When the "entering power save mode" problem appears running the latest KDE desktop on Ubuntu Linux 14.04, the monitor is disabled /PERMANENTLY/ by the operating system, and the following additional steps must be performed in order to reactivate the monitor:
1. Open a text mode terminal (CTRL-ALT-F1).
2. On the command line, logged in as the user running KDE, enter the following to delete all files in the KScreen configuration folder:
rm -f ~/.kde/share/apps/kscreen/*
3. Then reboot the computer. (Don't forget to disable DDC/CI on the monitor setup)
KDE bugreport: https://bugs.kde.org/show_bug.cgi?id=331900