Easily recreated problem. The scenario is just an example.  In this I use background as the culprit for ease but it could be any property.
1. Create a new jFrame form.
2. Add a panel and give it a background so you can see it.
3. Place a button on the panel.
4. Give jButton1 a background
5. Place another button on the panel.
6. Add a background to jButton2 by selecting "Value from existing component" then select jButton1 then background. Both buttons show the same background color.
7. Delete jButton1.
8. Close the form.
9. Reopen the form.  
10. The designer threw a null exception and the form can't be shown. The .form file contains an unresolvable link from jButton2 back to jButton1 which is now gone (<Component connection=jButton1 ... >). The code shows an error but in protected area and with the designer gone it's not easy to fix ... especially given that you have no clue as a user what happened and what to do about it.

Easy way out would be to catch the missing link rather than crash. More elegant would be to chain the links and resolve or warn when the key component is removed.