I ran the demo called Resize Map Shapes with Mouse Dragging (https://docs.telerik.com/devtools/wpf/controls/radmap/how-to/howto-resize-map-shapes-with-mouse-dragging)
which I downloaded from the associated web page (https://www.telerik.com/blogs/radmap-for-silverlight-wpf-how-to-resize-map-shapes-with-mouse-dragging)
and it worked fine.
I updated the controls to WPF40 version 2018.3.1016.40 and it it now acts differently. When dragging, it loses mouse capture. If I release the left mouse button and move the cursor back over the draggable circle it then continues to drag (won't do anything if I don't release the left mouse button).
I also tried this using WPF45 version 2018.3.1016.45 and the same problem (and changing my app's .Net version to 4.6.1).
Attached are two animated gifs showing the original version working and the replaced dll version's odd behavior.
I tracked GotMouseCapture, IsMouseCaptureChanged and LostMouseCapture and recorded this:
I didn't change the MainWindow.xaml.cs at all. I just removed the references to the 3 Telerik controls, removed the controls from the binaries folder, added the newer Telerik controls to the binaries folder, and added the references back. I'm using Visual Studio 2017.