TinyMCE body class not applied in OPE mode

Description

Steps to reproduce

1 Add following code to your solution.

[TinyMCEPluginNonVisual(AlwaysEnabled = true, PlugInName = "optimizededitor",
DynamicConfigurationOptionsHandler = typeof(OptimizedEditor), ServerSideOnly = true)]
public class OptimizedEditor : IDynamicConfigurationOptions
{
public IDictionary<string, object> GetConfigurationOptions()
{
return new Dictionary<string, object>
{
{ "body_class", "custom_body_class" }
};
}
}

2. Compile and run the application.
3. In OPE, open any page with an XHtml property.
4. Click the XHtml property to activate the TinyMCE editor.

Expected
The custom body class 'custom_body_class' is applied to the body node inside the editor's iframe body.

Actual
The custom body class 'custom_body_class' is not applied to the editor's iframe body.