Fix protectedTerms not stored due to weaklistener

CHANGELOG.md

@@ -25,6 +25,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 
 ### Fixed
 
+- We fixed an issue where custom "Protected terms" files were missing after a restart of JabRef [#8608](https://github.com/JabRef/jabref/issues/8608)
 - We fixed an issue where JabRef could not start due to a missing directory for the fulltex index [#8579](https://github.com/JabRef/jabref/issues/8579)
 - We fixed an issue where long article numbers in the `pages` field would cause an exception and preventing the citation style to display [#8381](https://github.com/JabRef/jabref/issues/8381), [citeproc-java](https://github.com/michel-kraemer/citeproc-java/issues/114)
 - We fixed an issue where online links in the file field were not detected correctly and could produce an exception [#8150](https://github.com/JabRef/jabref/issues/8510)

src/main/java/org/jabref/logic/protectedterms/ProtectedTermsPreferences.java

@@ -23,19 +23,19 @@ public ProtectedTermsPreferences(List<String> enabledInternalTermLists,
     }
 
     public ObservableList<String> getEnabledInternalTermLists() {
-        return FXCollections.unmodifiableObservableList(enabledInternalTermLists);
+        return enabledInternalTermLists;
     }
 
     public ObservableList<String> getEnabledExternalTermLists() {
-        return FXCollections.unmodifiableObservableList(enabledExternalTermLists);
+        return enabledExternalTermLists;
     }
 
     public ObservableList<String> getDisabledInternalTermLists() {
-        return FXCollections.unmodifiableObservableList(disabledInternalTermLists);
+        return disabledInternalTermLists;
     }
 
     public ObservableList<String> getDisabledExternalTermLists() {
-        return FXCollections.unmodifiableObservableList(disabledExternalTermLists);
+        return disabledExternalTermLists;
     }
 
     public void setEnabledInternalTermLists(List<String> list) {