1. Create new schema.
2. Switch to source view.
3. Type <xsd:element name=""/>
4. Type "in" between the quotes (text becomes <xsd:element name="in"/>) and
press Ctrl-Space.
Result: exception comes.
Further code completion calls may produce exceptions too.
Possibly exception appears when beginning of simple type name is typed.

java.lang.IllegalArgumentException: ancestor == descendant!!!
	at
org.netbeans.modules.editor.structure.api.DocumentModel.isDescendantOf(DocumentModel.java:274)
	at
org.netbeans.modules.editor.structure.api.DocumentModel.getChildren(DocumentModel.java:553)
	at
org.netbeans.modules.editor.structure.api.DocumentElement.getChildren(DocumentElement.java:281)
	at
org.netbeans.modules.xml.text.structure.XMLDocumentModelProvider.getDescendantsOfNotSkippedElements(XMLDocumentModelProvider.java:424)
	at
org.netbeans.modules.xml.text.structure.XMLDocumentModelProvider.generateDocumentElements(XMLDocumentModelProvider.java:402)
	at
org.netbeans.modules.xml.text.structure.XMLDocumentModelProvider.updateModel(XMLDocumentModelProvider.java:239)
	at
org.netbeans.modules.editor.structure.api.DocumentModel.updateModel(DocumentModel.java:436)
	at
org.netbeans.modules.editor.structure.api.DocumentModel.access$300(DocumentModel.java:106)
	at
org.netbeans.modules.editor.structure.api.DocumentModel$1.run(DocumentModel.java:420)
	at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:539)
[catch] at
org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:964)