nuclear warheads defy treaty?

This is more a question than a real diary, the data is clearly not in.  There's a report on CNN that there were nuclear warheads on a plane flying over the US.  This is apparently a violation of a treaty forbidding plane travel for nukes.  It's being billed as a mistake, but,. how can nuclear warheads be mistakenly placed on a military plane.  So, some questions:

Who told?
What was the ultimate destination?
and,
could this possibly be a whistle-blower who can't say all he or she knows, but who can say that there were nukes on a plane flying within the US?

Makes me wonder if nukes are being moved to be in place for those potential tactical nuclear first strikes in Iran.