CL_GUI_COLUMN_TREE Get selected nodes

Hi together,

i use the tree control of type CL_GUI_COLUMN_TREE in my report. After a user selected one or more nodes and push a button, i try to get all selected nodes with method GET_SELECTED_NODES and show the result with some more informations in a popup.

Now my problem. It the user starts the report first time, the method returns the correct number of selected nodes. If the user close the popup, change the selection of the nodes and open the popup again, the result of the methode GET_SELECTED_NODES is allways 0.

Has anybody a idea why?

Regards,

Anton