Recently in an article called "The Skyrme model" written by Zahed and Brown I've read that in pure QCD chiral perturbation theory (i.e., in theory with nonzero quark condensate due to attractive potential of passive gluon) some phenomena called "pentagonal anomaly" arises (p. 60). It in fact relates to imaginary part of effective chiral perturbative theory action. It is, like "usual" anomalies, scale-independent.
Could someone explain me why it is called "anomaly"? How it relates to the "usual" chiral anomaly?