Just because I’m curious I just had to keep trying.
And yes, I managed to re-create the error.
I added a new option “Alla lampor av” to the input_select.lights01 and reloaded Scripts and Automations. I had no automation calling this new option, but still I got an error in the log. And after restart - it’s back.
Once again with reference to wrong input_select (which is what is really strange):
2018-01-23 21:14:21 WARNING (MainThread) [homeassistant.components.input_select] Invalid option: Morgonbelysning av (possible options: Av, 22 grader auto, 24 grader auto, 24 grader max, 24 grader tyst)
The “Morgonbelysning av” is a reference to was previously was the first option in the input_select.
After my addition, “Alla lampor av” is the first option.
So if I try to create an explanation:
If you add a new option to an input_select and then reload scripts and/or automation, hass.io suddenly think that the previously first option in your first input_select belong to your other input_select. Which it doesn’t, and therefore it produces an error.
Phew. It doesn’t seem very likely, but now it has happened twice.
Now I know how to get rid of it, but it still seems like it would be worth investigating.