In the finals of a tournament today, the following interaction occurred:

-Player A controls a Lantern of Insight. The top card of Player B's library, an Island, is face-up.

-Player B activates his Scalding Tarn. He places the face-up Island onto the battlefield and picks up his deck to shuffle, clearly just taking a shortcut to the search.

-Player A stops him and tells him that, since Player B “found” the top card of the deck, he needs to reveal the new top card before he shuffles.

-Player B reveals a Serum Visions, returns it to the top of the deck, and proceeds with the shuffle. Once complete, he flips the new top card face-up, revealed by the Lantern. Play continues.

Is this correct, or did Player A trick Player B into giving away more information than necessary when he told him to reveal the Serum Visions?

The closest ruling I could find was the following, but it doesn't explicitly state what happens during the resolution of an ability:
401.6. Some effects tell a player to play with the top card of his or her library revealed, or say that a player may look at the top card of his or her library. If the top card of the player’s library changes while a spell is being cast, the new top card won’t be revealed and can’t be looked at until the spell becomes cast (see rule 601.2h). The same is true with relation to an ability being activated.

*EDIT* For ease of reference, the interaction is at 1:12:54: http://www.twitch.tv/magic2/v/15918183

Edited Nick Gajary (Sept. 14, 2015 02:16:42 PM)

Yes, Player A is correct. Since there is a (very) brief period of time in between the card being put onto the battlefield and the shuffle being performed, the next card in the library will be revealed for just a moment giving Player A a chance to see it.

As mentioned here, most players won't be aware of this and the potential for advantage is mostly nonexistent, so it's not something we're looking to punish heavily.