diff --git a/cps/admin.py b/cps/admin.py
index 5f9d0a0d..fea20ddc 100644
--- a/cps/admin.py
+++ b/cps/admin.py
@@ -1248,6 +1248,7 @@ def _db_configuration_update_helper():
             ub.session.query(ub.KoboReadingState).delete()
             ub.session.query(ub.KoboStatistics).delete()
             ub.session.query(ub.KoboSyncedBooks).delete()
+            helper.delete_thumbnail_cache()
             ub.session_commit()
         _config_string(to_save, "config_calibre_dir")
         calibre_db.update_config(config)
diff --git a/cps/fs.py b/cps/fs.py
index 0171a5d5..2f83378d 100644
--- a/cps/fs.py
+++ b/cps/fs.py
@@ -16,7 +16,6 @@
 #   You should have received a copy of the GNU General Public License
 #   along with this program. If not, see <http://www.gnu.org/licenses/>.
 
-from __future__ import division, print_function, unicode_literals
 from . import logger
 from .constants import CACHE_DIR
 from os import makedirs, remove
diff --git a/cps/helper.py b/cps/helper.py
index 7d7a4ae9..c8db50c2 100644
--- a/cps/helper.py
+++ b/cps/helper.py
@@ -1074,3 +1074,6 @@ def get_download_link(book_id, book_format, client):
 
 def clear_cover_thumbnail_cache(book_id):
     WorkerThread.add(None, TaskClearCoverThumbnailCache(book_id))
+
+def delete_thumbnail_cache():
+    WorkerThread.add(None, TaskClearCoverThumbnailCache(-1))
diff --git a/cps/tasks/thumbnail.py b/cps/tasks/thumbnail.py
index c0887e0a..31dc1f7b 100644
--- a/cps/tasks/thumbnail.py
+++ b/cps/tasks/thumbnail.py
@@ -214,6 +214,9 @@ class TaskGenerateCoverThumbnails(CalibreTask):
     def name(self):
         return 'GenerateCoverThumbnails'
 
+    def __str__(self):
+        return "GenerateCoverThumbnails"
+
     @property
     def is_cancellable(self):
         return True
@@ -421,6 +424,9 @@ class TaskGenerateSeriesThumbnails(CalibreTask):
     def name(self):
         return 'GenerateSeriesThumbnails'
 
+    def __str__(self):
+        return "GenerateSeriesThumbnails"
+
     @property
     def is_cancellable(self):
         return True
@@ -436,10 +442,12 @@ class TaskClearCoverThumbnailCache(CalibreTask):
 
     def run(self, worker_thread):
         if self.app_db_session:
-            if self.book_id:
+            if self.book_id > 0:    # make sure all thumbnails aren't getting deleted due to a bug
                 thumbnails = self.get_thumbnails_for_book(self.book_id)
                 for thumbnail in thumbnails:
                     self.delete_thumbnail(thumbnail)
+            else:
+                self.delete_all_thumbnails()
 
         self._handleSuccess()
         self.app_db_session.remove()
@@ -452,15 +460,28 @@ class TaskClearCoverThumbnailCache(CalibreTask):
             .all()
 
     def delete_thumbnail(self, thumbnail):
-        thumbnail.expiration = datetime.utcnow()
-
+        # thumbnail.expiration = datetime.utcnow()
         try:
-            self.app_db_session.commit()
             self.cache.delete_cache_file(thumbnail.filename, constants.CACHE_TYPE_THUMBNAILS)
+            self.app_db_session \
+                .query(ub.Thumbnail) \
+                .filter(ub.Thumbnail.type == constants.THUMBNAIL_TYPE_COVER) \
+                .filter(ub.Thumbnail.entity_id == thumbnail.entity_id) \
+                .delete()
+            self.app_db_session.commit()
         except Exception as ex:
             self.log.info(u'Error deleting book thumbnail: ' + str(ex))
             self._handleError(u'Error deleting book thumbnail: ' + str(ex))
 
+    def delete_all_thumbnails(self):
+        try:
+            self.app_db_session.query(ub.Thumbnail).filter(ub.Thumbnail.type == constants.THUMBNAIL_TYPE_COVER).delete()
+            self.app_db_session.commit()
+            self.cache.delete_cache_dir(constants.CACHE_TYPE_THUMBNAILS)
+        except Exception as ex:
+            self.log.info(u'Error deleting thumbnail directory: ' + str(ex))
+            self._handleError(u'Error deleting thumbnail directory: ' + str(ex))
+
     @property
     def name(self):
         return 'ThumbnailsClear'