Please include as much of the following information as possible to help me fix the bug:

Brief Description of Bug

The edgework for the icons are not being loaded, leaving a pure black square as icon backgrounds. Icons for items are also left as a hard-edged square.

Steps to Reproduce

Will occur while the setting "Hide icon backgrounds" is selected.
If you first select this, the edge work is still loaded. Thus you'd need to reload UI afterwards to see the problem.

Loaded Addons

Include a list of addons you were running at the time this bug occurred.

Back Trace (LUA Error Output)

No LUA errors.

This is expected behaviour.

Apologie for continued questions. Just need to verify.
The following image is a no-skin example of the same situation. Here you see the edgework remain.

So I guess my followup question would then be:

• Should the skin plugin not behave the same as standard?

Not really. The skin was setup that way intentionally - but admittedly it is a bit of a mixture of styles with the empty slot background setting being used as a proxy setting to toggle between them.