Product Version = NetBeans IDE Dev (Build 201110070600)
Operating System = Windows 7 version 6.1 running on amd64
Java; VM; Vendor = 1.7.0
Runtime = Java HotSpot(TM) 64-Bit Server VM 21.0-b17

- insert code
- Use entity manager

worked fine for the first time
and generated expected

@PersistenceContext(unitName="WebAppJUnitPU")
private EntityManager em;

(as part of the tuturial "testing unins embedded container)

After a problem, I changed some code. 
No, NB marks em as wrong. 
I deleted this code and tried to re-insert as abocve.
NetBeans generated this code instead:

    public void persist(Object object) {
        /* Add this to the deployment descriptor of this module (e.g. web.xml, ejb-jar.xml):
         * <persistence-context-ref>
         * <persistence-context-ref-name>persistence/LogicalName</persistence-context-ref-name>
         * <persistence-unit-name>WebAppJUnitPU</persistence-unit-name>
         * </persistence-context-ref>
         * <resource-ref>
         * <res-ref-name>UserTransaction</res-ref-name>
         * <res-type>javax.transaction.UserTransaction</res-type>
         * <res-auth>Container</res-auth>
         * </resource-ref> */
        try {
            Context ctx = new InitialContext();
            UserTransaction utx = (UserTransaction) ctx.lookup("java:comp/env/UserTransaction");
            utx.begin();
            EntityManager em = (EntityManager) ctx.lookup("java:comp/env/persistence/LogicalName");
            em.persist(object);
            utx.commit();
        } catch (Exception e) {
            Logger.getLogger(getClass().getName()).log(Level.SEVERE, "exception caught", e);
            throw new RuntimeException(e);
        }
    }


BTW NetBeans behavior nor is abnormal.
I inserted the code above by copy and paste.
In the meantime I copied and pasted some other code outside of NB.
Pasting here (or in NB editor) will still paste the same olld text :(
I really don't know what happened.
Sorry, I don't know how to reproduce it. The only thing I'm able to do, is to add some logs.

And, just now, after _cutting_ and copying, clipboard is ok inside NB works again. 
Dubious...