Yesterday at the club, we had this auction:
I (North) asked about the alert of 4
♦ at the time it was made. The explanation was "I don't know, it's either natural and weak, or a splinter)." After the auction, and before partner led, I asked if the explanation was correct, since West didn't seem disposed to say anything. He then said "we have no agreement". I called the TD. In the ensuing discussion, it came to light that West just wanted to "screw with their auction", although he did in fact have a splinter raise of spades. The TD said "you can't do that". West argued. TD repeated himself. Eventually West shut up, and the TD went away.
They didn't have an agreement. Like many pairs, they just checked the "splinter" box under responses to 1M, and never gave any thought to whether splinters apply in any other auction. Oh, the TD did say, while he was at the table, that "you have to have an agreement here".
They missed their slam.