codebrainz commented on this pull request.

@@ -53,6 +53,8 @@ public void plugin_init(Geany.Data data)

Alignment align; MultiTerm.Notebook notebook;

+ toplevel_widgets = new List<Widget>();

This probably needs to be assigned `null` in the cleanup function to avoid a leak in the GC and so there's no dangling junk left in it.