Hi,
My apologies for the delay in responding to you.
I was able to view the condition you have described here. We can set multiline text to the label by adding new line characters in the Label text.
Kindly review the code snippet,
// Creating Rectangle Node
Rectangle rect = new Rectangle(20, 100, 250, 250);
// Setting multiline text
rect.Labels.Add(new Label(rect, "MultiLine Label Text"));
rect.Labels[0].FontStyle.Bold = true;
rect.FillStyle.Color = Color.LightBlue;
this.diagram1.Model.AppendChild(rect);
Please take a look at the sample and let me know if it helps.
http://websamples.syncfusion.com/samples/Diagram.Windows/69871/main.htmRegards,
Suba