If a player controlled civilian unit loots a uniform from a dead soldier the soldiers uniform is duplicated and the civilian clothing disappears.

Sorry this is a bit of a long winded explanation but I believe the cause of this is as follows.

Most units are prevented from wearing a uniform belonging to any faction other than their own. To take the example of a BLUFOR player looting an OPFOR corpse. The BLUFOR player cannot loot the OPFOR uniform as they themselves are prevented from wearing the OPFOR uniform. In turn the OPFOR corpse is also prevented from receiving the BLUFOR uniform in exchange.

Civilians are able to wear any uniform. So, sticking with BLUFOR and OPFOR factions, if a civilian is wearing a BLUFOR uniform and attempts to loot an OPFOR uniform from an OPFOR unit's corpse, the civilian is able to receive the OPFOR uniform but the OPFOR corpse is unable to receive the BLUFOR uniform in exchange. This results in the BLUFOR uniform (and all inventory item) being destroyed and the OPFOR uniform (and all inventory items) being duplicated.