When the user:

• has 1 weapon equipped A and
• another weapon in his hands B and
• drags another weapon C onto MC inventory
• notices that weapon A that was initially on MC has disappeared.

Ex:MC has mosin equiped and crossbow in hand
drag and drop another weapon onto MC = mosin disappears

EDIT 01

• Weapon A (mosion in my case) appeared after on the ground after a server restart
• Droping Crossbow from MC inventory as makes it disappear on the ground!!!