When the Dangly Hoop Earrings item is equipped (which disables the head slot), the Shovel cannot be equipped second if the Earrings were equipped first. Which makes no sense why the shovel would need the cloak OR the helm slot.
However, if you equip the shovel first THEN equip the earrings, the log states the same error about disabled slots, but still lets you equip both.
I assume this is a bug so I'm reporting it here.
Same for "Chain of the Innate", an amulet that disables the head slot. It also disables Lisa's Holdables, so you can't equip a pipe at the same time. Except you can still equip it, somehow, visually, while it gets yanked out of the equipment slot.
This is also true for the Ironmind Circlet - a "cloak" that disables helm slot.
This is fixed.