Equip backpack bug

[mightydanp]

after i put a backpack on and then shift click another backpack on if you don't have armor on the other backpack goes into your armor slot and then disappears

[copygirl]

Vanilla "bug", can't prevent things from being equipped using shift-click without ASM magic. Backpacks return false for isValidArmor(), they're only meant to be equipped by sneaking and breaking the backpack block.