I will give you one example how Krishna sometimes breaks His promise. It is very nice story.
Krishna, when He joined Arjuna, He promised from His own side that "Because the fight is between your brothers, so it is not My duty... Because both of you are My relatives, so it is not My duty to join one party and not to join another. But because I have divided Myself—Myself, one side, and other side, My soldiers—but Duryodhana has decided to take My soldiers, not Me, so I shall join you. But I shall not fight. I shall not fight. I may take some work which may assist you."
So Arjuna offered, "Whatever work You like, You can take." So He said, "All right. I shall drive your chariot."
So Krishna's promise was that He will not fight. But at a time when Arjuna was perplexed by fighting with Bhisma... Bhisma was the greatest fighter, although he was very old man. Duryodhana incited him that "Because the other side are your very pet grandsons, you are not fighting fully." That was the complaint of Duryodhana. So in order to encourage him, Bhisma said to Duryodhana, "All right, tomorrow I shall finish all these five brothers. Tomorrow I shall finish. And I have got now special arrows for killing these five chivalrous brothers."
So Duryodhana was very intelligent. He told, "All right, please keep these five arrows with me for the night. I shall deliver you tomorrow in the morning." "All right, you take it." And Krishna understood. Krishna is, everything knows, past, present and future. Krishna knew it that "Bhisma has now promised. He will kill." So He asked Arjuna—this is also politics—that "You go to Duryodhana. Do you remember that Duryodhana"—Duryodhana is elderly than Arjuna—"that he would keep some promise which was offered to you?" Duryodhana told him, "Arjuna, whenever you want something, I shall give you." "Now this is the time. You can go." "And what is that?" "Now, he has got five arrows for killing you. You should take and come to Me."
So after fight, they were friends. So Arjuna went to the camp of Duryodhana, and he was well received. "Well Arjuna, come on. What do you want? Come on. Sit down. Do you want anything from me? If you want, I can stop this fight. I can return you this..." Arjuna said, "No. I have not come to you for begging my kingdom. Fighting will go on. But I want... You promised something." "Yes. I know. I offer you. What do you want?" "Now, I want those five arrows." At once he delivered.
And this information was carried to, I mean to say, Bhisma. Bhisma knew that "Krishna is very cunning also. He will save His devotee. So He has done this. All right, in spite of Krishna... He has broken my promise, and tomorrow I shall see. If Krishna does not break His promise, then His friend will be killed. I will fight in such a way."
So he was fighting in such a way that Arjuna became almost dead. Then at that time, Krishna... The chariot was torn into pieces, and Arjuna fell down. And then Krishna took up one of the wheel of the chariot and came before: "Now, Bhisma, you stop this fighting; otherwise I will kill you." Bhisma at once gave up his arrow, and he offered, "All right. Kill me."
So thing is that because Bhisma promised that "I shall kill Arjuna tomorrow," and Krishna also promised not to fight, just to save these two devotees, Arjuna and Bhisma—Bhisma also was a great devotee—just to show him that "I am breaking My promise. Please stop..." He wanted that "Either I shall break My promise or you shall kill Arjuna. So better see that I have broken My promise."
So in this way, sometimes, for devotee, He sometimes breaks His own promise.