[Janne] I Did the same steps below and it worked in 325. But when I opened object browser and viewed some class and continued from step 2 it bugged. It opened object browser after that sometimes and
 sometimes threw exception.

Steps:
1. Select Browsing workspace.
2. Close Object Browser.
3. Use command File|Object Browser to open it.
4. Object Browser is not opened. Exception is printed:

Exception occurred during event dispatching:
java.lang.IllegalStateException: Cannot initialize 0 th node of node com.netbeans.ide.nodes.AbstractNode@75a30f[Name=nul
l, displayName=null, handle=null] it already belongs to node com.netbeans.developer.impl.PackageNode@243f75[Name=Reposit
ory, displayName=Repository, handle=null]
        at com.netbeans.ide.nodes.Children.throwAlreadyUsedException(Children.java:542)
        at com.netbeans.ide.nodes.Children$6.run(Children.java:525)
        at com.netbeans.ide.util.Mutex.doEvent(Mutex.java:455)
        at com.netbeans.ide.util.Mutex.writeAccess(Mutex.java:240)
        at com.netbeans.ide.nodes.Children.initialize(Children.java:515)
        at com.netbeans.ide.nodes.Children.access$3(Children.java:513)

        at com.netbeans.ide.nodes.Children$5.run(Children.java:492)
        at com.netbeans.ide.util.Mutex.doEventAccess(Mutex.java:474)
        at com.netbeans.ide.util.Mutex.doReadAccess(Mutex.java:165)
        at com.netbeans.ide.util.Mutex.readAccess(Mutex.java:104)
        at com.netbeans.ide.nodes.Children.getNodes(Children.java:488)
        at com.netbeans.ide.explorer.view.ListView.updateList(ListView.java:478)
        at com.netbeans.ide.explorer.view.ListView.access$8(ListView.java:469)
        at com.netbeans.ide.explorer.view.ListView$9.run(ListView.java:404)
        at com.netbeans.ide.util.Mutex.doEvent(Mutex.java:455)
        at com.netbeans.ide.util.Mutex.readAccess(Mutex.java:146)
        at com.netbeans.ide.explorer.view.ListView.addNotify(ListView.java:395)
        at java.awt.Container.add