Here is the config ...

    "Use Teams": true,
    "Use Clans": true,
    "Use Friends": true,
    "Use Entity Owners": true,
    "Use Building Locks": false,
    "Use Tool Cupboards (Strongly unrecommended)": false,
    "Use Building Owners (You will need BuildingOwners plugin)": false,​

Try using "Use Entity Owners" : false
Can they remove any blocks they place ? or they cannot remove any blocks someone else places ?