how to prevent detaching links

I programatically generate a diagram with elements and links from a command language.
The user should be able to move the elements afterwards but not to detach links from elements.
I set RequiresConnections of the links to true but it's still possible to detach the link (if I select a link and move with the mouse to a link point the <--> sign appears and I can detach the link.
My application uses an older version of Diagram Studio (how can I see the version?) but I have a license of the newest version.

Kind regards, Rolf

Have you tried with the latest version?