For the entire of the harsher part of summer, i had to disable f.lux since it never got dark outside. F.lux would usually allocate 2-4 hours of red time, even if there was no night or twilight here. But thats a minor issue.
However:
During winter, f.lux really enjoys to transition at wrong times.Twilight ends almost a full hour before the sunrise, so f.lux would always be a hour late unless i set a location further south.
For sunset the same issue is there, F.lux would go to red about a hour before twilight actually happens.
It bothers me a lot.