@D.S.
So that means
A) Vietnam has the plane on radar turning around, and tried to tell Malaysia that day
B) Malaysia knew they had it on their radar at 2:40 in the Straights anyway
From what I remember reading, Vietnam ATC informed Malaysian ATC about the missing a/c at 02.40L (Malaysian time). This is pretty much exactly the time when the mystery a/c disappeared from the military radar to the west of Malaysia. I imagine the news sent the Malaysians scurrying to replay their recordings of what radar operators had failed to see? So there were two instances of '02.40', which may have confused a few people.