SUMMARY

When turning on the TV connected to the PC running Plasma, the video comes up in the wrong resolution (the highest resolution: 4096 X 2160 50Hz, not the correct resolution: 3840 X 2160 60 Hz) and even though the cursor is active, none of the other controls work.

The work around to fix the issue is to press CTRL-ALT-F1 for a console and then CTRL-ALT-F7 to re-init X, then the display is normalized.


STEPS TO REPRODUCE
1. Using an LG TV, Yamaha Receiver with video fed through, Nvidia Graphics with binary driver, install plasma, kde, etc.
2. Configure KDE to turn off the monitor after 3 minutes of no activity.
3. Turn off the TV and receiver.
4. Turn on the TV and receiver some time later (more than an hour?)
5. Turn on the receiver and TV (not sure what order, I should do more testing. I'm using a smart remote).

OBSERVED RESULT
The display comes up in 4096 by 2160 50 Hz instead of 3840 X 2160 60 Hz and the screen is not usable.


EXPECTED RESULT
The screen should exit power saving / power down cleanly. This only happens when the TV and receiver are turned off.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Kernel 4.9X through 5.1.3  
(available in About System)
KDE Plasma Version: 5.14.5
KDE Frameworks Version: 5.57.0
Qt Version: 5.11.3

ADDITIONAL INFORMATION

Please ask questions and suggest ways to get more information.

This may not be related to power, it may be KDE improperly restoring the monitor resolution based on the highest resolution available in EDD instead of what's specified in the X config files. But it could be a lot of things.