In each case, Christ's admonition is that we should have a healthy skepticism of miracles because miracles may produce deception. It is not that the miracle does not occur. The more important point is, does it witness to the truth? Does it witness to the ultimate reality, the will of God?
In both Jesus' instruction in the New Testament (Matthew 24:24; 7:22-23; Revelation 13:13-14) and in Moses' teaching in the Old Testament (Deuteronomy 13:1-5), it is clear—regardless of the wonder done—if a person even implies that we are free to disobey God, the miracle is not a demonstration of God's truth. A miracle it was, but it does not validate God's truth.
We must be especially skeptical of those who say that they believe in keeping God's laws, and then turn right around and say that the Sabbath and holy days are no longer necessary and that "true Christians" can keep Christmas, Easter, Halloween, etc. But they "believe" that they are to keep God's laws! It is especially deceptive because so many of such people are really nice individuals.