If the system uses a mixture of local time, local date, UTC time, and UTC date for different purposes, crossing the International Date Line could create some scenarios that would not exist under any other circumstance.
As to why local time would be used for anything on such a system, I don't know, but Windows does base some things off local midnight. If the system time zone is adjusted when the aircraft moves from place to place (instead of being permanently set to UTC+0) and attempts to derive UTC from local time, that could wreak all sorts of havoc.
See, that's just it. Local time just isn't all that useful, and probaby gets in the way. Think about it... on any sortie it's not unlikely at all that the plane could cross back and forth several times across the local zone boundary. Shifting the system time an hour up and down each time would just be confusing.
Sure, maybe there's a ~clock~ display that can have a local zone adjustment, but beyond that there's no purpose to it.
Of course... in new systems bugs will happen. Sometimes it's the *really* simple bugs that nobody thinks to look for. But this story isn't making any sense yet. But we'll see.
The F-22 uses Windows!?...Oh, nooooooo, we're all dooooooomed!!