DBGrid and Drag'n Drop


I've a DBGrid on Form1 and a TreeView on Form2.

The Grid has two columns, first a simply integer-value-field,
the second is connected with a persistent Lookup-Field.
Now when I drag an item of the TreeView to this second
column, the text is shown correctly in the right Cell of Column No. 2,
 but it seems to me, that the Lookup-Field doesn't recognize it.

Also I set the value of the Lookup-Field directly

MyDataModule.LookupField.Value := TTreeView(Source).Selected.Text;

in the DBGrid's DragDrop-Event, the same thing happens
as described above.

Can somebody tell me, what I've done wrong and how is the
right implementation of drag and drop between a TreeView
and a DBGrid?

Thanks and regards