diff --git a/src/calibre/gui2/library/models.py b/src/calibre/gui2/library/models.py
index 01f597caf4..a2555cfc56 100644
--- a/src/calibre/gui2/library/models.py
+++ b/src/calibre/gui2/library/models.py
@@ -156,8 +156,7 @@ class BooksModel(QAbstractTableModel): # {{{
             self.cover_cache.stop()
         self.cover_cache = CoverCache(db, FunctionDispatcher(self.db.cover))
         self.cover_cache.start()
-        self.metadata_backup = MetadataBackup(db,
-                self.db.dump_metadata)
+        self.metadata_backup = MetadataBackup(db)
         self.metadata_backup.start()
         def refresh_cover(event, ids):
             if event == 'cover' and self.cover_cache is not None:
diff --git a/src/calibre/library/caches.py b/src/calibre/library/caches.py
index e675c97c76..bc16681f81 100644
--- a/src/calibre/library/caches.py
+++ b/src/calibre/library/caches.py
@@ -22,12 +22,17 @@ from calibre.ebooks.metadata import title_sort
 from calibre import fit_image, prints
 
 class MetadataBackup(Thread): # {{{
+    '''
+    Continuously backup changed metadata into OPF files
+    in the book directory. This class runs in its own
+    thread and makes sure that the actual file write happens in the
+    GUI thread to prevent Windows' file locking from causing problems.
+    '''
 
-    def __init__(self, db, dump_func):
+    def __init__(self, db):
         Thread.__init__(self)
         self.daemon = True
         self.db = db
-        self.dump_func = dump_func
         self.keep_running = True
         from calibre.gui2 import FunctionDispatcher
         self.do_write = FunctionDispatcher(self.write)
@@ -47,7 +52,7 @@ class MetadataBackup(Thread): # {{{
 
             dump = []
             try:
-                self.dump_func([id_], dump_queue=dump)
+                self.db.dump_metadata([id_], dump_to=dump)
             except:
                 prints('Failed to get backup metadata for id:', id_, 'once')
                 import traceback
@@ -55,7 +60,7 @@ class MetadataBackup(Thread): # {{{
                 time.sleep(2)
                 dump = []
                 try:
-                    self.dump_func([id_], dump_queue=dump)
+                    self.db.dump_metadata([id_], dump_to=dump)
                 except:
                     prints('Failed to get backup metadata for id:', id_, 'again, giving up')
                     traceback.print_exc()
diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index 8c34510de4..39770068bb 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -567,7 +567,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
         return self.field_metadata[key]
 
     def dump_metadata(self, book_ids=None, remove_from_dirtied=True,
-            commit=True, dump_queue=None):
+            commit=True, dump_to=None):
         'Write metadata for each record to an individual OPF file'
         if book_ids is None:
             book_ids = [x[0] for x in self.conn.get(
@@ -583,11 +583,11 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
             raw = metadata_to_opf(mi)
             path = os.path.join(self.abspath(book_id, index_is_id=True),
                     'metadata.opf')
-            if dump_queue is None:
+            if dump_to is None:
                 with open(path, 'wb') as f:
                     f.write(raw)
             else:
-                dump_queue.append((path, raw))
+                dump_to.append((path, raw))
             if remove_from_dirtied:
                 self.conn.execute('DELETE FROM metadata_dirtied WHERE book=?',
                         (book_id,))