Sounds like the fun I had checking flight status recently. Many airline websites make you enter a lot of information, and exactly, to get flight status these days... I suspect to avoid "terrorists" knowing where the planes are.

Anyway, try entering the information for a flight that leaves late at night, say, 11:30pm PST. Some airlines will require you to choose "tomorrow" as the time for it, even though it's still "today" when it happens. Their computer system knowns what day it is, and can't seem to handle overlaps, even though, seemingly, this should come up a lot more than midnight movie showings do...