Describe the bug

When an element with connectors is copied from one diagram to another, deleting that element on the second diagram will delete the connectors on the first.

To Reproduce

Steps to reproduce the behavior:

1. Create a new SysML project to get the SysML example
2. Change Preference to not Remove Unused Elements
3. Open the diagram Functional Boundary Behavior
   
4. In the model, right-click on Activity and choose New Diagram -> New Activity Diagram
   
5. Click within Functional Boundary Behavior and select all with keyboard
   
6. Copy with keyboard
7. Click within New Activity Diagram and paste with Keyboard
   
8. In New Activity Diagram, delete the action "Determine Actuator Command"
   
9. View "Functional Boundary Behavior". Notice connections are now missing.
   

Expected behavior

Connections are not deleted from the original diagram

Screenshots

Interspersed within the steps

OS

• Linux (Please put in notes the specific distro)
• macOS
• Windows

Version

Version of Gaphor: 2.21.1

Additional information

Add any other context about the problem here.