Reproduced in build 060711.

To reproduce the bug:

- create a new schema;
- switch to Source view;
- add 'attributeGroup'
    <xsd:attributeGroup name="sasa">
        <xsd:anyAttribute/>
        <xsd:annotation>
            <xsd:documentation>Documentation</xsd:documentation>
        </xsd:annotation>
    </xsd:attributeGroup>
- switch to Schema view and check results;
- switch back to Source view and delete 'annotation';
- switch to Schema view 
- 'annotaion' is not removed from model.

Delete 'annotation' from Schema view.

Exception:
java.lang.AssertionError
	at org.netbeans.modules.xml.xdm.XDMModel$6.update(XDMModel.java:559)
	at org.netbeans.modules.xml.xdm.XDMModel.mutate(XDMModel.java:337)
	at org.netbeans.modules.xml.xdm.XDMModel.mutate(XDMModel.java:289)
	at org.netbeans.modules.xml.xdm.XDMModel.remove(XDMModel.java:563)
	at org.netbeans.modules.xml.xdm.xam.XDMAccess.removeChild(XDMAccess.java:210)
	at
org.netbeans.modules.xml.xam.dom.AbstractDocumentComponent.removeChild(AbstractDocumentComponent.java:434)
	at
org.netbeans.modules.xml.xam.dom.AbstractDocumentComponent.removeChildQuietly(AbstractDocumentComponent.java:272)
	at
org.netbeans.modules.xml.xam.dom.AbstractDocumentComponent.removeChildQuietly(AbstractDocumentComponent.java:49)
	at
org.netbeans.modules.xml.xam.AbstractComponent._removeChildQuietly(AbstractComponent.java:115)
	at
org.netbeans.modules.xml.xam.AbstractComponent.setChild(AbstractComponent.java:383)
	at
org.netbeans.modules.xml.xam.AbstractComponent.setChildBefore(AbstractComponent.java:370)
	at
org.netbeans.modules.xml.schema.model.impl.SchemaComponentImpl.setAnnotation(SchemaComponentImpl.java:101)
	at
org.netbeans.modules.xml.schema.model.impl.xdm.SyncUpdateVisitor.visit(SyncUpdateVisitor.java:734)
	at
org.netbeans.modules.xml.schema.model.impl.AnnotationImpl.accept(AnnotationImpl.java:72)
	at
org.netbeans.modules.xml.schema.model.impl.xdm.SyncUpdateVisitor.update(SyncUpdateVisitor.java:60)
	at
org.netbeans.modules.xml.schema.model.impl.xdm.SyncUpdateVisitor.update(SyncUpdateVisitor.java:48)
	at
org.netbeans.modules.xml.schema.model.impl.xdm.SyncUpdateVisitor.update(SyncUpdateVisitor.java:31)
	at
org.netbeans.modules.xml.xam.dom.AbstractDocumentModel.removeChildComponent(AbstractDocumentModel.java:289)
	at
org.netbeans.modules.xml.schema.ui.nodes.SchemaComponentNode.destroy(SchemaComponentNode.java:697)
	at
org.openide.explorer.ExplorerActionsImpl$DeleteActionPerformer.doDestroy(ExplorerActionsImpl.java:620)
	at
org.openide.explorer.ExplorerActionsImpl$DeleteActionPerformer.performAction(ExplorerActionsImpl.java:570)
	at
org.openide.explorer.ExplorerActionsImpl$DeleteActionPerformer.actionPerformed(ExplorerActionsImpl.java:631)
	at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1634)
	at javax.swing.JComponent.processKeyBinding(JComponent.java:2824)
	at javax.swing.JComponent.processKeyBindings(JComponent.java:2870)
	at javax.swing.JComponent.processKeyEvent(JComponent.java:2787)
	at java.awt.Component.processEvent(Component.java:5776)
	at java.awt.Container.processEvent(Container.java:1984)
	at java.awt.Component.dispatchEventImpl(Component.java:4407)
	at java.awt.Container.dispatchEventImpl(Container.java:2042)
	at java.awt.Component.dispatchEvent(Component.java:4237)
	at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1828)
	at
java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:693)
	at
java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:952)
	at
java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:824)
	at
java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:657)
	at java.awt.Component.dispatchEventImpl(Component.java:4279)
	at java.awt.Container.dispatchEventImpl(Container.java:2042)
	at java.awt.Window.dispatchEventImpl(Window.java:2405)
	at java.awt.Component.dispatchEvent(Component.java:4237)
[catch] at java.awt.EventQueue.dispatchEvent(EventQueue.java:600)
	at
java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
	at
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)