I have a Web base application running on JBoss 3.2.1. A value object is always initialized, updated, and deleted through a stateless session EJB. The value object uses HashMap object as container to hold different kind of objects as value collection, which could be simple as String object, or a composite object. Everything is fine during the first 2 hours of JBoss server running, but after 2 hours the value collection HashMap always contain some non-expected objects (wrong object). Same logic but behavior differently based on the timing. Is it possible that 'new HashMap()' won't always return a clean collection type object after JBoss running for a while?