RT itinerary to TYO display on AA website:

Outbound mid-day departure flight labeled "overnight flight" even though it was flown entirely during daylight.

Inbound flight did not have this "overnight" label, even though it was a late afternoon departure with most of the flight during nighttime.

Lazy IT programming (arrival date not equal to departure date) and/or confounding use of "overnight" as substitute for date change, it would appear.