Dear devrant community, I have a question...

For perspective, a few years ago, we had an incident, where one dev was looking for other employment, he did not say anything, he was just looking, and ended up accepting an offer, handing in his resignation and all that. But there was another dev doing the same thing, but he informed management that he was thinking of leaving, and would be attending interviews... Personally I note difference in treatment of the dev that was honest, he was slightly getting phased out and getting the cold shoulder most of the time combined with weird kindness that was cearly not sincere, where the other dev was given a hard time for not saying anything about them looking for other opportunities, and treated as though they betrayed all the trust they had earned and no longer deserved to be trusted....

My question is, what, in your opinion, is the right thing to do when you are looking for a new opportunity? Do you tell management, or is it actually none of their business?