FloatingWindow has no Close button

When calling DocumentWindow.Float(), the window is successfully floated and a Close button available in the title bar. However on deserializing no Close button is available?

Here is the serialized layout...

<DockSiteLayout xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" SerializationFormat="All" Version="2">
<AutoHideHost />
<Content xsi:type="Workspace">
<Content xsi:type="TabbedMdiHost">
<Content xsi:type="TabbedMdiContainer" SelectedWindowUniqueId="f5150f47-c5bf-40e4-8ed3-8498272f6aa6">
<UIElement xsi:type="DocumentWindowRef" UniqueId="f5150f47-c5bf-40e4-8ed3-8498272f6aa6" />
</Content>
</Content>
</Content>
<DocumentWindows>
<DocumentWindow UniqueId="afddf977-46c0-4f61-a57a-05643471123c" SerializationId="Page8ee4d41e079b445eade0d8b8be2ad36c" IsOpen="true" State="Document" />
<DocumentWindow UniqueId="f5150f47-c5bf-40e4-8ed3-8498272f6aa6" SerializationId="Page4554d1528925439cbbda4f60d548eac5" IsOpen="true" State="Document" />
</DocumentWindows>
<RaftingHosts>
<RaftingHost UniqueId="a2ee4274-dd49-484d-a3b7-efacb712ab9c" IsMaximized="true" Location="1672,-8" Size="1678,933">
<AutoHideHost />
<Content xsi:type="Workspace">
<Content xsi:type="TabbedMdiHost">
<Content xsi:type="TabbedMdiContainer" SelectedWindowUniqueId="afddf977-46c0-4f61-a57a-05643471123c">
<UIElement xsi:type="DocumentWindowRef" UniqueId="afddf977-46c0-4f61-a57a-05643471123c" />
</Content>
</Content>
</Content>
</RaftingHost>
</RaftingHosts>
</DockSiteLayout>