diff --git a/beets/library.py b/beets/library.py
index 91034df90..1b08cb571 100644
--- a/beets/library.py
+++ b/beets/library.py
@@ -281,11 +281,12 @@ class FlexModel(object):
     def __setitem__(self, key, value):
         """Assign the value for a field.
         """
-        if key in self._fields:
-            self._values_fixed[key] = value
-        else:
-            self._values_flex[key] = value
-        self._dirty.add(key)
+        source = self._values_fixed if key in self._fields \
+                 else self._values_flex
+        old_value = source.get(key)
+        source[key] = value
+        if old_value != value:
+            self._dirty.add(key)
 
     def update(self, values):
         """Assign all values in the given dict.
@@ -344,6 +345,11 @@ class LibModel(FlexModel):
     """The flex field SQLite table name.
     """
 
+    _bytes_keys = ('path', 'artpath')
+    """Keys whose values should be stored as raw bytes blobs rather than
+    strings.
+    """
+
     def __init__(self, lib=None, **values):
         self._lib = lib
         super(LibModel, self).__init__(**values)
@@ -355,7 +361,7 @@ class LibModel(FlexModel):
         """
         if not self._lib:
             raise ValueError('{0} has no library'.format(type(self).__name__))
-        if not self._id:
+        if not self.id:
             raise ValueError('{0} has no id'.format(type(self).__name__))
 
     def store(self):
@@ -372,7 +378,7 @@ class LibModel(FlexModel):
                 value = self[key]
                 # Wrap path strings in buffers so they get stored
                 # "in the raw".
-                if key == 'path' and isinstance(value, str):
+                if key in self._bytes_keys and isinstance(value, str):
                     value = buffer(value)
                 subvars.append(value)
         assignments = assignments[:-1]  # Knock off last ,
@@ -1727,7 +1733,7 @@ class Album(LibModel):
             self._lib.move(item, copy, basedir=basedir, with_album=False)
 
         # Move art.
-        self.move_art(self._lib, copy)
+        self.move_art(copy)
 
     def item_dir(self):
         """Returns the directory containing the album's first item,
diff --git a/test/test_db.py b/test/test_db.py
index d01798c42..744933049 100644
--- a/test/test_db.py
+++ b/test/test_db.py
@@ -533,21 +533,21 @@ class DisambiguationTest(unittest.TestCase, PathFormattingMixin):
     def test_unique_with_default_arguments_uses_albumtype(self):
         album2 = self.lib.get_album(self.i1)
         album2.albumtype = 'bar'
-        self.lib._connection().commit()
+        album2.store()
         self._setf(u'foo%aunique{}/$title')
         self._assert_dest('/base/foo [bar]/the title', self.i1)
 
     def test_unique_expands_to_nothing_for_distinct_albums(self):
         album2 = self.lib.get_album(self.i2)
         album2.album = 'different album'
-        self.lib._connection().commit()
+        album2.store()
 
         self._assert_dest('/base/foo/the title', self.i1)
 
     def test_use_fallback_numbers_when_identical(self):
         album2 = self.lib.get_album(self.i2)
         album2.year = 2001
-        self.lib._connection().commit()
+        album2.store()
 
         self._assert_dest('/base/foo 1/the title', self.i1)
         self._assert_dest('/base/foo 2/the title', self.i2)
@@ -561,6 +561,8 @@ class DisambiguationTest(unittest.TestCase, PathFormattingMixin):
         album2.year = 2001
         album1 = self.lib.get_album(self.i1)
         album1.albumtype = 'foo/bar'
+        album2.store()
+        album1.store()
         self._setf(u'foo%aunique{albumartist album,albumtype}/$title')
         self._assert_dest('/base/foo [foo_bar]/the title', self.i1)
 
@@ -757,6 +759,7 @@ class AlbumInfoTest(unittest.TestCase):
     def test_albuminfo_stores_art(self):
         ai = self.lib.get_album(self.i)
         ai.artpath = '/my/great/art'
+        ai.store()
         new_ai = self.lib.get_album(self.i)
         self.assertEqual(new_ai.artpath, '/my/great/art')
 
@@ -906,9 +909,10 @@ class PathStringTest(_common.TestCase):
         self.assert_(isinstance(dest, str))
 
     def test_artpath_stores_special_chars(self):
-        path = 'b\xe1r'
+        path = b'b\xe1r'
         alb = self.lib.add_album([self.i])
         alb.artpath = path
+        alb.store()
         alb = self.lib.get_album(self.i)
         self.assertEqual(path, alb.artpath)