Hi Stephan,
I have created a sample as per your specifications, and have attached it .Here I have created node in the Form2,when the node is allowed to get transferd to the Main Form,the node will get displayed or else it get ignored. Please refer to it and let me know if this helps you. If not, kindly modify it to show the problem and send it back to us so that this issue could be investigated accurately.
Thanks for your interest in Syncfusion products.
Kind Regards,
Deepa.
CreatingOrEditingNode.zip