I wonder if Mormons dismiss anything Joseph Smith was wrong about!
We do not hold our prophets to be infallible, kid. Joseph Smith once said, "A prophet is a prophet only when acting as such." And Brigham Youn later added, "We are all liable to err and many may think that a man in my standing ought to be perfect; no such thing." In other words, not everything an LDS prophet says is to be considered revelation from God, nor was that the case in the Old Testament. Prophets (ancient and modern) are human beings who are entirely capable of being wrong. They can also have their own opinions about things, some of which they may voice from time to time.
You seem to be of the opinion that the prophets in the Bible never made any prophesies that did not come to pass. If you were to hold them to the same standard you hold Joseph Smith to, you'd have quite a few false prophets on your hands.
Clearly the free-will of men plays a role in whether or not prophecy is fulfilled exactly as stated. For example:
God told David that the men of Keilah “will deliver thee up [to Saul]” (1 Samuel 23:12). This didn't take place. Why? Because David fled from the city.
God told Ezekiel that the city of Tyre would be destroyed by Nebuchadrezzar and would never be rebuilt. Nebuchadrezzar did lay siege against Tyre, but was unable to take the city. God then told Ezekiel that since Nebuchadrezzar had not taken Tyre, he would be given Egypt. Again, while Nebuchadrezzar did win a battle against an Egyptian army in battle, he never conquered Egypt either.
Isaiah prophesied that the Medes would slay men, women and children and that Babylon would “be as when God overthrew Sodom and Gomorrah. It shall never be inhabited, neither shall it be dwelt in from generation to generation” (Isaiah 13:17-20). In 539 B.C., Cyrus, Babylon was taken by the Medes without bloodshed. The city became a major city of the empire and remained inhabited for hundreds of years.