  Anomalous monopole of disk shape is found to exist in the semiclassical
theory of a two-mode interacting boson system. The quantum origin of this
anomaly is the collapsing or bundling of field lines of Berry curvature caused
by the interaction between bosons in the semiclassical limit. The significance
of this anomalous monopole is twofold: (1) it signals the failure of the von
Neumann-Wigner theorem in the semiclassical limit; (2) it indicates a breakdown
of the correspondence principle between quantum and classical dynamics.
