Make sure that you are using the classname from CfgWeapons, CfgMagazines or CfgGlasses! Placing an item in Eden Editor places the container of the item, not the item itself.
To get the item classname you can open the config of the placed container in the Config Viewer and look for a subclass called "TransportItems".
The correct classname is stored under configFile >> "CfgVehicles" >> _containerClass >> "TransportItems" >> "some_classname" >> "name".