When equipping the "Rat Master Mask" to the "Hat" trinket slot, it will occasionally duplicate itself into other trinket slots. This is especially noticeable with mods that add many other trinket slots, such as Spectrum.

It seems to be more likely to occur when quick moving ("shift-clicking") the item into its trinket slot.

Actually, this may just be a problem with creative mode in my particular modpack, since I just had the same thing happen with a netherite hoe???

EDIT: It's a known issue with Trinkets (the mod) when in creative mode. Though how it happened with a hoe is beyond me.