Empty _shadowLayers?

I’m playing with the Obj-C filter plugin example w/ 2.4.1, and the filter template code isn’t working for me.

When the filter gets invoked, the example code tries to iterate over _shadowLayers. My understanding is that this a temporary copy of the selected layers that the filter is supposed to operate on.

But, what I’m seeing in the debugger is that _shadowLayers is empty, but _layers is not. Has the plugin API changed, or am I misunderstanding something? This happens both when I call the plugin from Edit view or from Font view.

I haven’t changed the template code at all (except to change a couple CheckSelection references to _checkSelection.)