Restore background before draw/blit in on_release of draggable legend

Author: vittoboa

lib/matplotlib/offsetbox.py

@@ -1506,6 +1506,7 @@ def on_release(self, event):
             self.finalize_offset()
             self.got_artist = False
             if self._use_blit:
+                self.canvas.restore_region(self.background)
                 self.ref_artist.draw(
                     self.ref_artist.figure._get_renderer())
                 self.canvas.blit()