Fix album store method to cascade flex field deletions to items

beets/library.py

@@ -1355,9 +1355,12 @@ class Album(LibModel):
         """
         # Get modified track fields.
         track_updates = {}
-        for key in self.item_keys:
-            if key in self._dirty:
+        track_deletes = set()
+        for key in self._dirty:
+            if key in self.item_keys:
                 track_updates[key] = self[key]
+            elif key not in self:
+                track_deletes.add(key);
 
         with self._db.transaction():
             super().store(fields)
@@ -1366,6 +1369,12 @@ class Album(LibModel):
                     for key, value in track_updates.items():
                         item[key] = value
                     item.store()
+            if track_deletes:
+                for item in self.items():
+                    for key in track_deletes:
+                        if key in item:
+                            del item[key]
+                    item.store()
 
     def try_sync(self, write, move):
         """Synchronize the album and its items with the database.

docs/changelog.rst

@@ -133,6 +133,8 @@ Bug fixes:
 * :doc:`/plugins/fromfilename`: Fix failed detection of <track> <title>
   filename patterns.
   :bug:`4561` :bug:`4600`
+* Fix issue where deletion of flexible fields on an album doesn't cascade to items
+  :bug:`4662`
 
 For packagers:
 

test/test_library.py

@@ -77,6 +77,19 @@ class StoreTest(_common.LibTestCase):
         self.i.store()
         self.assertTrue('composer' not in self.i._dirty)
 
+    def test_store_album_cascades_flex_deletes(self):
+        album = _common.album()
+        album.flex1="Flex-1"
+        self.lib.add(album)
+        item = _common.item()
+        item.album_id = album.id
+        item.flex1="Flex-1"
+        self.lib.add(item)
+        del album.flex1
+        album.store()
+        self.assertNotIn('flex1', album)
+        self.assertNotIn('flex1', album.items()[0])
+
 
 class AddTest(_common.TestCase):
     def setUp(self):