Code inspection: Inconsistent synchronization on field

public class LockingSample
{
  private readonly List<object> _resources = new List<object>();
  private readonly object _lockObject = new object();

  public void AddResource(object resource)
  {
    lock (_lockObject)
      _resources.Add(resource);
  }

  public void RemoveResource(object resource)
  {
    // Warning: The field is sometimes used inside synchronized block
    // and sometimes used without synchronization
    if (_resources.Contains(resource))
    {
      _resources.Remove(resource);
    }
  }
}