EditorDescriptor on shared blocks not executing

I want to extend the group container for my block but when adding a EditorDescriptor it's executed when I use it as a local block but not as a shared block. What's the difference and how can I accomplish this with a shared block?

[EditorDescriptorRegistration(TargetType = typeof(MyBlock))]
public class MyBlockEditorDescriptor : EditorDescriptor
{
	public override void ModifyMetadata(ExtendedMetadata metadata, IEnumerable attributes)
	{
		base.ModifyMetadata(metadata, attributes);
		metadata.Properties.Cast().First().GroupSettings.ClientLayoutClass = "MyBlockContainer";
	}
}