What does dictionary really store as a value in C#?

Question

I'm using a specific datasource from devexpress called VirtualServerMode. It's a read-only datasource by default. To enable ability to edit data I need to pass collection implementing the IList interface.

I use Dictionary to store different collections.

When I create collection in this way:

Using constructor to initialize the dictionary

protected AbstractRepository()
{
    _className = typeof(TCardType).Name;
    _acquireList = new Dictionary<string, BindingList<TCardType>>();
    _acquireList[_className] = new BindingList<TCardType>();
}

And the property returns the value

   public BindingList<TCardType> AcquireList => _acquireList[_className];

The Devexpress component does not recognize the collection and edit mode is not enabled.

If I initialize the dictionary in like this

public IList GreateAcquireList()
{
    var outcome = new BindingList<TCardType>();
    _acquireList[_className] = outcome;
    return outcome;
}

And pass the collection to the datasource

private void FileCardDatasource_AcquireInnerList(object sender, VirtualServerModeAcquireInnerListEventArgs e)
{
    e.InnerList = Report.GreateAcquireList();
}

The component recognises the collection and edit mode is enabled.

Why does the dictionary not return a reference to the reference type value?