It stands to reason that there would be anomalies in magic, as in science, really. Some examples of scientific anomalies to cite? Glad you asked! Bumblebees! It is impossible, according to the laws of aerodynamics, for them to fly. But no one told the bumblebees that, and so they do. Also, nothing is supposed to travel faster than the speed of light. However. Quantum physicists have discovered a particle that seemingly DOES travel faster than light: the tachyon.

Neither Muggles nor Wizards know everything about their world, and so there will always be anomalies.