Planning tool daylight warning anomaly

Hi - ever since the graphical planning tool has been added to SGP, I have noticed that the daylight warning is not triggered consistently:
For instance, during the spring, as the onset of darkness is little later each night, I will set the start and stop times one night, both within the hours of darkness.
A week later I may resume the sequence and bring up the planning tool. Although the start time is now in the daylight period, no warning is shown, but if I increment the start time by a minute, the warning pops up.

I don’t think this needs a log file as it is 100% consistent behavior.