Screw Eclipse... and packages... and IDE... no, wait... screw me!
Just a note to myself – always check what classes are you importing in IDE, because if you see @Singleton in your class, it doesn’t mean it will work as a EJB Singleton. In my case it wasn’t referencing to javax.ejb.Singleton as I assumed, but com.sun.jersey.spi.resource.Singleton. Wasted 2 hours of looking for the answer or issue in a glassfish-3.1 JIRA. Did I mention I should always check the exact package of the imported class…?...