Hi Donna,
With regards to Problem when Add/remove and change offset y of nodes at runtime on a manual layout diagram, after analyzing the provided sample we came to know that you are using the Frames for Navigation.
Frame:
Frame is a content control that provides the ability to navigate to and display content. Frame can be hosted within other content, as with other controls and elements.
Problem:
Frame does not store an instance of a content object in navigation history. Instead, Frame creates a new instance of the content object each time it is navigated to by using navigation history. This behavior is designed to avoid excessive memory consumption when large numbers and large pieces of content are being navigated to. Consequently, the state of the content is not remembered from one navigation to the next.
The similar thing is happened when clicking the Button for Navigating to Diagram, it creates new diagramControl (after adding the Newnode).
For storing a state for a piece of content in navigation history, please refer to the following link.
About Frames:
http://msdn.microsoft.com/en-us/library/ms750478.aspx#CookiesNavigation History:
http://msdn.microsoft.com/en-us/library/system.windows.navigation.customcontentstate.aspxPlease let us know if you have any concerns.
Regards,
Ramya