Created Unassigned: Zoombox customization [20723]

When I try to re-style the zoom box control (Object->Change Style->Change a copy). Blend 2013 returns me this error: "Missing key in the object "InputBindingCollection"".

Inner Exception StackTrace:
in System.Xaml.XamlObjectWriter.GetKeyFromInstance(Object instance, XamlType instanceType, IAddLineInfo lineInfo)
in System.Xaml.XamlObjectWriter.Logic_DoAssignmentToParentCollection(ObjectWriterContext ctx)
in System.Xaml.XamlObjectWriter.Logic_DoAssignmentToParentProperty(ObjectWriterContext ctx)
in System.Xaml.XamlObjectWriter.WriteEndObject()
in System.Xaml.XamlWriter.WriteNode(XamlReader reader)
in System.Windows.Markup.WpfXamlLoader.TransformNodes(XamlReader xamlReader, XamlObjectWriter xamlWriter, Boolean onlyLoadOneNode, Boolean skipJournaledProperties, Boolean shouldPassLineNumberInfo, IXamlLineInfo xamlLineInfo, IXamlLineInfoConsumer xamlLineInfoConsumer, XamlContextStack`1 stack, IStyleConnector styleConnector)
in System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)

What am I doing wrong?
Thank you
Lorenzo