diff --git a/src/calibre/db/cache.py b/src/calibre/db/cache.py
index 80b925e770..82ed243a14 100644
--- a/src/calibre/db/cache.py
+++ b/src/calibre/db/cache.py
@@ -2351,9 +2351,15 @@ class Cache:
 
     @read_api
     def split_if_is_multiple_composite(self, f, v):
+        '''
+        If f is a composite column lookup key and the column is is_multiple then
+        split comma-separated v into unique non-empty values. The uniqueness
+        comparison is case-insensitive. If values are case-insensitive equals
+        then the last is returned.
+        '''
         fm = self.field_metadata.get(f, None)
         if fm and fm['datatype'] == 'composite' and fm['is_multiple']:
-            return [v.strip() for v in v.split(',') if v.strip()]
+            return list({v.strip().lower() : v.strip() for v in v.split(',') if v.strip()}.values())
         return v
 
     @read_api
diff --git a/src/calibre/gui2/dialogs/quickview.py b/src/calibre/gui2/dialogs/quickview.py
index 2a17db7c2d..3fcaa0e7c6 100644
--- a/src/calibre/gui2/dialogs/quickview.py
+++ b/src/calibre/gui2/dialogs/quickview.py
@@ -542,10 +542,9 @@ class Quickview(QDialog, Ui_Quickview):
         self.books_table.setRowCount(0)
 
         mi = self.db.new_api.get_proxy_metadata(book_id)
-        vals = mi.get(key, None)
-        if self.fm[key]['datatype'] == 'composite' and self.fm[key]['is_multiple']:
-            sep = self.fm[key]['is_multiple'].get('cache_to_list', ',')
-            vals = [v.strip() for v in vals.split(sep) if v.strip()]
+        print('aaa', key, mi.get(key, None))
+        vals = self.db.new_api.split_if_is_multiple_composite(key, mi.get(key, None))
+        print('bbb', vals)
         try:
             # Check if we are in the GridView and there are no values for the
             # selected column. In this case switch the column to 'authors'