Major Description
BooleanQuery caches its hashcode on the grounds that it is immutable. However, this immutability doesn't hold if some of its clauses hold queries that are not themselves immutable - for example, a MultiTermQuery with a changeable rewrite method. If one of these clauses is mutated after the hashcode has been calculated, then the next time the parent BooleanQuery is used the assertion in BooleanQuery.hashCode() will fail.