Close tab should check for unsaved changes

When editing a document, I add some text to the title and wait for 10 seconds. I click outside the field and wait another then seconds. Then I click the close icon on the tab and expect a "save changes" warning, but I don't get it. Instead, the document is closed and my changes are gone.

Logs say:
27.03.2009 15:07:24 ERROR [org.hippoecm.repository.jackrabbit.AbstractFacetSearchProvider.populate():234] facet value with only facet type constant found. Skip
result
27.03.2009 15:07:27 WARN [org.hippoecm.frontend.editor.plugins.field.FieldPlugin.updateProvider():114] Unknown field body in type defaultcontent:article
27.03.2009 15:07:27 ERROR [org.hippoecm.repository.jackrabbit.AbstractFacetSearchProvider.populate():234] facet value with only facet type constant found. Skip
result
27.03.2009 15:07:42 WARN [org.hippoecm.frontend.plugins.standards.browse.BrowseService.browse():128] Model null is not an JcrNodeModel
27.03.2009 15:07:42 ERROR [org.apache.jackrabbit.jcr2spi.hierarchy.ChildNodeEntriesImpl.update():186] ChildInfo iterator contains multiple entries with the same
name|index or uniqueID -> ignore ChildNodeInfo.
27.03.2009 15:07:42 ERROR [org.apache.jackrabbit.jcr2spi.hierarchy.ChildNodeEntriesImpl.update():186] ChildInfo iterator contains multiple entries with the same
name|index or uniqueID -> ignore ChildNodeInfo.