Hi Nicklas,
Thank you for your interest in Syncfusion products.
Whenever you create a symbol in "Symbol Designer" the symbol will be Grouped automatically. Thus you might not have able to access the text in the symbol through code easily. Currently the BitmapNode does not support labels and we have a open feature request for it.
To overcome this issue please create a BitmapNode and TextNode and Group them together. To know more about grouping, go through the following online document.
http://help.syncfusion.com/ug_71_new/diagram/Grouping.htmlPlease let me know if you have any questions.
Regards,
Dinesh